Hm. Not sure, I haven't ever done that.
But I do know that the MP3 files are just more files like the FID index files. The index file is the one ending in the number "1" and the actual data is the file ending in the number "0". For instance, on my player, the actual MP3 file of Tom Sawyer is "/drive0/fids/bf90" and the song's index/tag data is stored in "/drive0/fids/bf91".
The files that end in "1" are just ascii data containing the song or playlist information. For instance, on my player, /drive0/fids/bf91 looks like this:
(from what is a fid?
I would have figured that the purpose of MP3toFID was to do that particular processing on everything for you. I guess not?