Looking in the operators manual the following says: " WARNING TO THE OPERATOR. In early releases of the Revenge from Mars game code ROMs, DO NOT perform the Disable Updated Code. Doing so will cause your game to run in free only mode and the UPDATE GAME CODE utility menu will not allow the updated game code to be enabled. If you accidentally disable the update game code, do the following:

1) Plug a keyboard into the keyboard port (located near the computer case in the backbox) or
2) plug a computer terminal into  the COM 1 port (located near the coin door).
Then at the command line (%) prompt type the following:
% fupdate enable
to re-enable the Updated game code.
Note: This operation takes about 15 seconds to complete."
It also states that if you disable the update the system will run the version of the game code located on the prism card.
Hope this helps.