build X up by Y

[gaborsch]

In many languages we have the += and -= operators, that increment or decrement a certain variable with a certain value. I think it would be great feature if we could introduce it in Rockstar, too. I recommend the following syntax to consider for such an operation:

Build X up by Y
Knock X down by Y

This would be a natural extension the current syntax of Build X up, up, up by allowing the by keyword instead of the second up. This would not mix other possible uses of the by keyword.
The expression for Y could be any expression - just like in other programming languages.