I started working on this yesterday because I needed to repair some tags in a huge number of files... Anyway, it's taking too much time and hair (and I don't have much of either left) so I'm attaching it here, in case anyone has an interest in learning a little c++ along with id3lib and wxGTK. It looks like it's old enough to be somewhat out-of-date in all three of the above areas; from what I can tell, it should work (eventually) with wxGTK-2.6 if anyone ever gets that far.
Created attachment 191728 [details] Preliminary ebuild Shell of an ebuild (still needs an epatch line for the relevant patch).
Created attachment 191729 [details, diff] Partial patch to build with newer toolchain (gcc 4.3.3). This is incomplete, but it's a start...
I'm thinking it was a bad idea to even post this one (stinky code that it is) so I won't complain if you decide to close it...
