My usual knee-jerk response is to suggest that you use JET as that what it's designed for.
For this specific case, however, you might be better off just writing a simple popup action (use the new plugin project with the popup action template) that parses the properties file (looks simple enough to do in Java) and writes out the target code to another file, the console or, if you're clever, back into an existing file in the right place.
Once you have the plugin generated for you with the template, the rest should be simple Java.