I was just thinking today how it might be kind of cool if someone could hack the Altered Beast cartridge ROM to use SELECT as a duplicate Jump button. That way people with three button pads could use Button III for jumping instead of pressing UP on the D-pad.
What would be even cooler is if all the buttons were changed, so that Button I could be jump, and Button II and III (SELECT) would be the punch and kick attacks.
I'm no coder so I have no idea how much work this might involve, but it'd be a neat project. I'd certainly use the resulting ROM on my flash cart to play the game on my system.