Script Triggers - Popup Menu (field changes)
While FileMaker formally lacks an event model (causing actions based on user events - mouse over, mouse down, etc.), it doesn't mean you can't figure out how make this type of functionality happen. A lot of articles on this site talk about using a script triggering plug-in to accomplish this.
Using a script triggering plug-in, I show you how to fire scripts when selections are made from a Pop-up menu or Drop-down list. Beyond that, the important thing to note is that it's based on any field change. Yes, you're right, it's based on an auto-enter calculation.
The unique feature that's shown in this video however, is how you can use any number of scripts tied to any of the possible options. Meaning a status field can be set to "PAID" and Script X will fire. Change that value to "DELINQUENT" and it fires Script Z. Unlimited scripts to match an unlimited number of options.
Think about all the cool things you can make happen when a field value is changed to a matched target value.