Modified Contra Cart & Ring
This is how I did it. In short, I bought Contra, dumped the ROM, hex edited the file, flashed it to a new ROM chip and soldered it all back together. Took some work but worth it. I changed player names to ours and also changed the ending text to ask her once she beat the game. She said yes! And to the purists who cringe when they see a hacked up cart... relax, it was for a good cause! ;-)
this cart rebuild is pretty easy to do, in fact... more people should play around with this stuff IMO, and you could even make a little business selling custom or hard-to-find carts to your friends, or at conventions. all the ROM dumps are already online.