1. Find out what the next available fid number is. You've got a sortable list of them now, right, so that should be easy.
2. Create your new fid files using that number. There's a 0 file and a 1 file for each fid of course.
3. Inside one of the two fid files put the ASCII data such as the name of the fid (look at another example of a fid file to see the format). I forget if this is the 0 file or the 1 file, but you'll see when you look at one of the examples.
4. Inside the other fid file put a list of what sub-fids (playlists and/or songs) you want your new playlist to contain. Again, look at your examples for the format and to determine whether it's the 0 or the 1 file.
5. Whatever playlist you want this new playlist contained in, then you have to snag that fid and add your fid to its list.
6. Put your two files and the one altered parent fid back onto the player.
7. Force a manual database rebuild.
I think that's all. Anyone got any corrections?