New RFS file

dd if=/dev/zero of=/path/to/factoryfs.rfs bs=4096 count=66560
losetup /dev/loop0 /path/to/factoryfs.rfs
fat.format -S 4096 -s 1 -F 32 /dev/loop0
mount -t vfat /dev/loop0 /mnt/wherever

#Edit files

umount /dev/loop0
losetup -d /dev/loop0

#To make it easier to edit in the future
#mount
mount -t vfat -o loop=/dev/loop0 /path/to/factoryfs.rfs /mnt/wherever
#unmount
umount /path/to/factoryfs.rfs