Just copy models/default.ini to modelXX.ini in the models folder on the Tx usb disk. You have to do this on your computer. I don't think there's a hard-wired limit on how many you can have, as it's not clear if you'll run out of disk for files or ram to hold file names during a load/save first.
Do not ask me questions via PM. Ask in the forums, where I'll answer if I can.
My remotely piloted vehicle ("drone") is a yacht.