For FBA, change command on es_systems.cfg to:
COMMAND=/home/pi/RetroPie/supplementary/runcommand/runcommand.sh 1 “/home/pi/RetroPie/emulators/pifba/fba2x %ROM%”
You can use roms from an usb, change rom folder on the same file like this:
i got an issue with this, the system generates a folder called roms for easy copying roms to the raspberry, if you put roms here it will be copyed to sd. I dont know how to disable this, but if you keep roms folder empty, and make another directory like “games”, you can leave roms here.