Perl's regexp are a language on their own, if you REALLY˛ allow the full spectrum of features this is not imaginable for me.°

I'm sure there are some computer science theorems proving this. (probably Halting problem?)

The only way I could see is with a restricted rules language, which is translated to regexp later.

Most likely a XY Problem ...

... monitoring if newly added rules also match already matched filenames and raising an alarm should be good enough.

°) as a side note, you can also embed Perl-code in regexes

˛) from arbitrary sources ... that's crazy