From what I can gather there shouldn't be a problem. Putting in a game that requires a keycode should not stop it from working. Where you would have a problem is if you changed the keycode to a game you didn't have. Then you would be be stuck.
If you lived in Europe I could have reflashed it. Obviously I could do America but the postage would probably too much.
Okay, so I'll officially declare that I will reflash people's broken AR/GS cartridges, if they pay postage both ways and include a pack of sweets from your region of the world