I have not tried this but can you have more than one game on the arduboy at a time?
No. There is not enough memory.
it is possible someone could write 2 or 3 small games built into 1 that could be uploaded but standard games need to be uploaded one at a time.
I’m sure version 2 of the ArduBoy will have an SD Card so you can store your entire game library on it.
I only know of one game that does this: Puzzle Pack by @Atomic