I found a bug/cheat back in the day on my Genesis. I read in a magazine about some game that'd glitch in a cheating fashion if you put in Altered Beast, waited for the title screen to come up, then yanked it out with the power still on, put in the next game, and hit restart. I didn't have that game, but I tried it with Strider, I'm not sure why, but it worked! You now had unlimited lives, but you had to play on the hardest difficulty setting! That was actually the first way I beat the game, though...
I know, this sounds like one of those stupid things you hear someone claim worked, but doesn't, but truly, it worked! And I never fried my Genesis doing it, though the Genesis certainly didn't seem happy about having the cartridge ripped out in mid-load...