There's an easy way to get another chance: come back on a new pseudonym, and avoid whatever problematic behaviors and areas that led to your being blocked/banned in the first place -- or, even avoid anything that might lead people to realize you're the same person. If your editing is beneficial to the project, and avoids old prowling grounds, it's probably unlikely that anybody will make the link between your new account and your old one(s). If you want to help, just come in, lay low, and help out.
If, on the other hand, you come back and keep causing problems, or repeatedly use socks to demand redemption, somebody's likely to make the connection, and another block will probably result. Repeatedly mashing your head is certainly a popular method, but what I've personally seen in community after community suggests it's not very likely to work, on the web. Better to just start a new identity and build a better reputation from scratch.
That's my opinion, anyway. -Luna