If you use RipEnc to encode, ID3 tag, and database your MP3 files, you may find that the list of possible genres it gives you don’t match the genres in your music collection. The genres presented are built into a command-line utility called id3ren, and represent the list of genres accepted by ID3.org, in addition to some new genres added by the WinAmp folks.
If you need genres not on that list, download the id3ren source code , open the file genre.h, and edit as needed. Recompile by typing

 make mv id3ren ~/config/bin 

Keep the source handy in case your replacement id3ren binary ever gets overwritten.