diff --git a/.vortex/.ahoy.yml b/.vortex/.ahoy.yml
index 55e1af10e..c6b246931 100644
--- a/.vortex/.ahoy.yml
+++ b/.vortex/.ahoy.yml
@@ -37,10 +37,14 @@ commands:
   lint:
     name: Lint Vortex project.
     cmd: |
+      ahoy lint-installer
       ahoy lint-scripts
       ahoy lint-dockerfiles
       ahoy test-docs
 
+  lint-installer:
+    cmd: composer --working-dir installer lint
+
   lint-scripts:
     cmd: ./tests/lint.scripts.sh
 
diff --git a/.vortex/installer/src/Command/InstallCommand.php b/.vortex/installer/src/Command/InstallCommand.php
index b1f186dc2..c20a7a09d 100644
--- a/.vortex/installer/src/Command/InstallCommand.php
+++ b/.vortex/installer/src/Command/InstallCommand.php
@@ -368,6 +368,7 @@ protected function replaceTokens(): void {
       'webroot',
       'profile',
       'provision_use_profile',
+      'theme',
       'database_download_source',
       'database_image',
       'override_existing_db',
diff --git a/.vortex/installer/src/Traits/PromptsTrait.php b/.vortex/installer/src/Traits/PromptsTrait.php
index 018ac9919..045ed834f 100644
--- a/.vortex/installer/src/Traits/PromptsTrait.php
+++ b/.vortex/installer/src/Traits/PromptsTrait.php
@@ -179,6 +179,23 @@ protected function processDatabaseDownloadSource(string $dir): void {
     }
   }
 
+  protected function processTheme(string $dir): void {
+    $webroot = $this->getAnswer('webroot');
+    $name = $this->getAnswer('theme');
+
+    File::fileReplaceContent('/DRUPAL_THEME=.*/', 'DRUPAL_THEME=' . $name, $dir . '/.env');
+
+    $file_dst = $this->findThemeFile($this->config->getDstDir(), $webroot);
+    // Do not update the theme files if it is not a theme from the Vortex
+    // template.
+    if (!empty($file_dst) && !$this->isVortexTheme(dirname($file_dst))) {
+      $file_tmpl = $this->findThemeFile($dir, $webroot);
+      if (!empty($file_tmpl)) {
+        File::rmdirRecursive(dirname($file_tmpl));
+      }
+    }
+  }
+
   protected function processDatabaseImage(string $dir): void {
     $image = $this->getAnswer('database_image');
     File::fileReplaceContent('/VORTEX_DB_IMAGE=.*/', 'VORTEX_DB_IMAGE=' . $image, $dir . '/.env');
@@ -531,33 +548,66 @@ protected function discoverValueProfile(): ?string {
   protected function discoverValueTheme(): ?string {
     $webroot = $this->getAnswer('webroot');
 
+    $name_from_env = NULL;
     if ($this->isInstalled()) {
-      $name = $this->getValueFromDstDotenv('DRUPAL_THEME');
-      if (!empty($name)) {
-        return $name;
+      $name_from_env = $this->getValueFromDstDotenv('DRUPAL_THEME');
+    }
+
+    $file = $this->findThemeFile($this->config->getDstDir(), $webroot);
+
+    if (empty($file)) {
+      // If theme file was not found, but the theme is set in the .env file -
+      // return the theme name from the .env file.
+      return $name_from_env ?: NULL;
+    }
+
+    $name_from_info = str_replace(['.info.yml', '.info'], '', basename($file));
+
+    // Check that this is a theme coming originally from the Vortex template.
+    $dir = dirname($file);
+
+    if (!$this->isVortexTheme($dir)) {
+      // If the theme is not coming from the Vortex template - return the theme
+      // name from the .env file.
+      return $name_from_env ?: NULL;
+    }
+
+    if ($name_from_env) {
+      if ($name_from_info !== $name_from_env) {
+        // If the theme name from the .env file does not match the theme name
+        // from the theme file - return the theme name from the info file
+        // to update the .env file.
+        return $name_from_info;
       }
+
+      return $name_from_env;
     }
 
+    return NULL;
+  }
+
+  protected function findThemeFile(string $dir, string $webroot): ?string {
     $locations = [
-      $this->config->getDstDir() . sprintf('/%s/themes/custom/*/*.info', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/themes/custom/*/*.info.yml', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/sites/all/themes/custom/*/*.info', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/sites/all/themes/custom/*/*.info.yml', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/profiles/*/themes/custom/*/*.info', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/profiles/*/themes/custom/*/*.info.yml', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/profiles/custom/*/themes/custom/*/*.info', $webroot),
-      $this->config->getDstDir() . sprintf('/%s/profiles/custom/*/themes/custom/*/*.info.yml', $webroot),
+      sprintf('%s/%s/themes/custom/*/*.info', $dir, $webroot),
+      sprintf('%s/%s/themes/custom/*/*.info.yml', $dir, $webroot),
+      sprintf('%s/%s/sites/all/themes/custom/*/*.info', $dir, $webroot),
+      sprintf('%s/%s/sites/all/themes/custom/*/*.info.yml', $dir, $webroot),
+      sprintf('%s/%s/profiles/*/themes/custom/*/*.info', $dir, $webroot),
+      sprintf('%s/%s/profiles/*/themes/custom/*/*.info.yml', $dir, $webroot),
+      sprintf('%s/%s/profiles/custom/*/themes/custom/*/*.info', $dir, $webroot),
+      sprintf('%s/%s/profiles/custom/*/themes/custom/*/*.info.yml', $dir, $webroot),
     ];
 
-    $name = File::findMatchingPath($locations);
-
-    if (empty($name)) {
-      return NULL;
-    }
+    return File::findMatchingPath($locations);
+  }
 
-    $name = basename($name);
+  protected function isVortexTheme(string $dir): bool {
+    $c1 = file_exists($dir . '/scss/_variables.scss');
+    $c2 = file_exists($dir . '/Gruntfile.js');
+    $c3 = file_exists($dir . '/package.json');
+    $c4 = File::fileContains('build-dev', $dir . '/package.json');
 
-    return str_replace(['.info.yml', '.info'], '', $name);
+    return $c1 && $c2 && $c3 && $c4;
   }
 
   protected function discoverValueDomain(): ?string {
diff --git a/.vortex/installer/src/Traits/TuiTrait.php b/.vortex/installer/src/Traits/TuiTrait.php
index 8eef2b218..05b08304e 100644
--- a/.vortex/installer/src/Traits/TuiTrait.php
+++ b/.vortex/installer/src/Traits/TuiTrait.php
@@ -333,6 +333,14 @@ protected function askForAnswer(string $name, string $question): void {
 
   /**
    * Process answers.
+   *
+   * @param string $name
+   *   Name of the answer.
+   * @param string $dir
+   *   Temporary directory where processing takes place.
+   *
+   * @return mixed
+   *   Processed answer.
    */
   protected function processAnswer(string $name, string $dir): mixed {
     return $this->executeCallback('process', $name, $dir);
diff --git a/.vortex/tests/bats/_helper.bash b/.vortex/tests/bats/_helper.bash
index a4f6e5573..70b0ac3ed 100644
--- a/.vortex/tests/bats/_helper.bash
+++ b/.vortex/tests/bats/_helper.bash
@@ -234,6 +234,7 @@ assert_files_present_common() {
   local suffix_abbreviated_camel_cased="${4:-Sw}"
   local suffix_camel_cased="${5:-StarWars}"
   local webroot="${6:-web}"
+  local assert_theme="${7:-1}"
 
   local suffix_abbreviated_uppercase="$(string_to_upper "${suffix_abbreviated}")"
 
@@ -254,7 +255,7 @@ assert_files_present_common() {
   # Assert that Vortex footnote remains.
   assert_file_contains "README.md" "This repository was created using the [Vortex](https://github.com/drevops/vortex) project template"
 
-  assert_files_present_drupal "${dir}" "${suffix}" "${suffix_abbreviated}" "${suffix_abbreviated_camel_cased}" "${suffix_camel_cased}" "${webroot}"
+  assert_files_present_drupal "${dir}" "${suffix}" "${suffix_abbreviated}" "${suffix_abbreviated_camel_cased}" "${suffix_camel_cased}" "${webroot}" "${assert_theme}"
 
   popd >/dev/null || exit 1
 }
@@ -453,6 +454,7 @@ assert_files_present_drupal() {
   local suffix_abbreviated_camel_cased="${4:-Sw}"
   local suffix_camel_cased="${5:-StarWars}"
   local webroot="${6:-web}"
+  local assert_theme="${7:-1}"
 
   pushd "${dir}" >/dev/null || exit 1
 
@@ -480,27 +482,29 @@ assert_files_present_drupal() {
   assert_file_exists "${webroot}/modules/custom/${suffix_abbreviated}_search/${suffix_abbreviated}_search.info.yml"
 
   # Site theme created.
-  assert_dir_exists "${webroot}/themes/custom/${suffix}"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/js/${suffix}.js"
-  assert_dir_exists "${webroot}/themes/custom/${suffix}/scss"
-  assert_dir_exists "${webroot}/themes/custom/${suffix}/images"
-  assert_dir_exists "${webroot}/themes/custom/${suffix}/fonts"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/.gitignore"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.info.yml"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.libraries.yml"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.theme"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/Gruntfile.js"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/package.json"
-
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Unit/${suffix_camel_cased}UnitTestBase.php"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Unit/ExampleTest.php"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Kernel/${suffix_camel_cased}KernelTestBase.php"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Kernel/ExampleTest.php"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Functional/${suffix_camel_cased}FunctionalTestBase.php"
-  assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Functional/ExampleTest.php"
-
-  # Comparing binary files.
-  assert_binary_files_equal "${LOCAL_REPO_DIR}/web/themes/custom/your_site_theme/screenshot.png" "${webroot}/themes/custom/${suffix}/screenshot.png"
+  if [ "${assert_theme}" = 1 ]; then
+    assert_dir_exists "${webroot}/themes/custom/${suffix}"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/js/${suffix}.js"
+    assert_dir_exists "${webroot}/themes/custom/${suffix}/scss"
+    assert_dir_exists "${webroot}/themes/custom/${suffix}/images"
+    assert_dir_exists "${webroot}/themes/custom/${suffix}/fonts"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/.gitignore"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.info.yml"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.libraries.yml"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/${suffix}.theme"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/Gruntfile.js"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/package.json"
+
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Unit/${suffix_camel_cased}UnitTestBase.php"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Unit/ExampleTest.php"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Kernel/${suffix_camel_cased}KernelTestBase.php"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Kernel/ExampleTest.php"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Functional/${suffix_camel_cased}FunctionalTestBase.php"
+    assert_file_exists "${webroot}/themes/custom/${suffix}/tests/src/Functional/ExampleTest.php"
+
+    # Comparing binary files.
+    assert_binary_files_equal "${LOCAL_REPO_DIR}/web/themes/custom/your_site_theme/screenshot.png" "${webroot}/themes/custom/${suffix}/screenshot.png"
+  fi
 
   # Drupal Scaffold files exist.
   assert_file_exists "${webroot}/.editorconfig"
diff --git a/.vortex/tests/bats/install.existing.bats b/.vortex/tests/bats/install.existing.bats
index 99efdb038..682217b6e 100644
--- a/.vortex/tests/bats/install.existing.bats
+++ b/.vortex/tests/bats/install.existing.bats
@@ -308,7 +308,7 @@ load _helper.bash
   assert_file_contains ".env.local" "some random content"
 }
 
-@test "Install into existing: previously installed project; custom webroot; discovery; quiet" {
+@test "Install into existing: previously installed bespoke project; custom webroot; discovery; quiet" {
   echo "VORTEX_WEBROOT=rootdoc" >>".env"
 
   # Populate current dir with a project at current version.
@@ -323,8 +323,8 @@ load _helper.bash
   assert_files_present_common "" "" "" "" "" "rootdoc"
 }
 
-@test "Install into existing: previously installed project; custom theme; discovery; quiet" {
-  echo "DRUPAL_THEME=star_wars" >>".env"
+@test "Install into existing: previously installed bespoke project; custom named theme; discovery; quiet" {
+  echo "DRUPAL_THEME=star_wars" >> ".env"
 
   # Populate current dir with a project at current version.
   output=$(run_installer_quiet)
@@ -338,6 +338,28 @@ load _helper.bash
   assert_files_present_common
 }
 
+@test "Install into existing: previously installed project; bespoke theme; discovery; quiet" {
+  # Populate current dir with a project at current version.
+  output=$(run_installer_quiet)
+  assert_output_contains "WELCOME TO VORTEX QUIET INSTALLER"
+  assert_output_not_contains "It looks like Vortex is already installed into this project"
+
+  assert_git_repo
+
+  install_dependencies_stub
+
+  # Replace the theme with a custom one.
+  rm -Rf "web/themes/custom/star_wars"
+  mktouch "web/themes/custom/star_wars/star_wars.info.yml"
+
+  output=$(run_installer_quiet)
+  assert_output_contains "WELCOME TO VORTEX QUIET INSTALLER"
+  assert_output_contains "It looks like Vortex is already installed into this project"
+
+  assert_files_present_common "" "" "" "" "" "" 0
+  assert_file_not_exists "web/themes/custom/star_wars/Gruntfile.js"
+}
+
 @test "Install into existing: previously installed project; custom profile; discovery; quiet" {
   # Populate current dir with a project at current version.
   output=$(run_installer_quiet)
diff --git a/.vortex/tests/bats/install.parameters.bats b/.vortex/tests/bats/install.parameters.bats
index aa6eee60d..5d13cb586 100644
--- a/.vortex/tests/bats/install.parameters.bats
+++ b/.vortex/tests/bats/install.parameters.bats
@@ -403,7 +403,7 @@ load _helper.bash
 }
 
 #
-# Helper to create fixture files to fake pre-installed state.
+# Helper to create fixture files to fake pre-installed state from Vortex.
 #
 # Note that this helper provides only one state of the fixture site.
 #
@@ -426,7 +426,12 @@ fixture_preinstalled() {
 
   # Sets 'theme' to 'resisting'.
   mktouch "${webroot}/sites/all/themes/custom/resisting/resisting.info.yml"
+  mktouch "${webroot}/sites/all/themes/custom/resisting/Gruntfile.js"
+  mktouch "${webroot}/sites/all/themes/custom/resisting/scss/_variables.scss"
+  mktouch "${webroot}/sites/all/themes/custom/resisting/package.json"
+  echo "build-dev" >>"${webroot}/sites/all/themes/custom/resisting/package.json"
   mktouch "${webroot}/sites/all/themes/custom/yetanothertheme/yetanothertheme.info.yml"
+  echo "DRUPAL_THEME=resisting" >>.env
 
   # Sets 'ci_provider' to 'GitHub Actions'.
   mktouch ".github/workflows/build-test-deploy.yml"