Are you talking about Gp32 modz? If I recall correctly someone asked this a while ago. Anyways here are the following mods I know of that has tutorials.
cobbleware.com
emuholic.emuboards.com
reloded.com
Make MODS for BOR GP32 is the same that make MODS for PC/DREAM/XBOX/PS2 etc...
Just download BOR_EDIT from BOR page. That include instruccions & sample level demo.
If you have specific troubles just ask here.