I'm wondering if there is a way to use a variable from a list I'm using in my script as part of the right boundary for a new variable extraction I need to create using regex and groups.
If you switch to Advanced mode in the variable extractor panel you can use NeoLoad variable in your regular expression.
So yes you can use a variable as part of your right boundary.
Be careful the variable is not evaluated when you define your extractor so you won't see your result right away but it will evaluated during the runtime.