Unfortunately, I haven't had time to do a proper guide so I'll have to just give you a quick overview of how to edit the main screen games.
Use something like WinImage to open the vendor.img file. The files you are interested in are:
Code:
\res\local\English\games.ini - Edit the entry for the game you want to swap and point it to the new game
\res\roms\ - Add the new game rom zip file here
\res\image\games\ - Folder for each game containing the icons
There is also a cache folder, but I would suggest trying a small game first that doesn't need a cache, like Puzzle Bobble or League Bowling. I'll add the extra information about cache when I can.
For now, don't even mess with icons. Just add the rom, example lbowling.zip to the roms folder. Then edit games.ini and change one of the entries
Example
Code:
[GAME]
[ID]=0
[TYPE]=3
[NAME]=AGGRESSORS OF DARK KOMBAT
[DIR]=aodk
Change it to
Code:
[GAME]
[ID]=0
[TYPE]=5
[NAME]=LEAGUE BOWLING
[DIR]=lbowling
Then save and flash. If it works then you can make it nice with proper icons etc. If it doesn't then you might not be using the proper FBA romset.
Note: If you're like me then the first thing you want to do when you open the vendor.img is delete the "hack" folder. I have zero interest in emulating other systems on my Neo Geo.