It needs to be graphical. No sed, awk, grep, perl, whatever. I know how to use those and I do use them now, but I need to cherry-pick each replace in 300+ files.
I want
I think regexxer is exactly what you're looking for:
regexxer is a nifty GUI search/replace tool featuring Perl-style regular expressions. If you need project-wide substitution and you’re tired of hacking sed command lines together, then you should definitely give it a try.
See also the screenshot, looks a lot like what you're describing: