If you have defined a fill-in variable, you can change its value in the Input form, when the template is executed, and the output generated by PhraseExpander will adapt automatically.

You may also want to change the value of a variable (either text or user-input) by code, for example when a certain condition is met, or to increment it by a certain value (this is great to compute scores).

You can do that by using the Update variable macro.