This sounds like a perfect use case for object oriented programming. “I want something mostly like that thing that already exists, but with a slight variation.“

This sounds like a perfect use case for object oriented programming. “I want something mostly like that thing that already exists, but with a slight variation.“ Or hooks, if you’re one of those weird Lisp programmers. Unfortunately, virtually all regex engines I’ve ever seen were an opaque black box with no ability to modify the functionality at all.