Changing IP address

Well, I was allowed to re-join a site I had been banned from, but their chatbox still has my IP banned and they cant get it to unban without the admin (who's not online a lot)

I know HOW to change my IP address, I just want to know if it's going to screw anything up, block me from sites or anything like that. Or will it just log me out of sites I'm already logged into and I'll just have to re-login?

Changing your IP address shouldn't have any adverse effects; in fact, it most likely won't even log you out of any sites (saved logins are typically stored in cookies). Many Internet Service Providers regularly switch IP addresses around.

Just send them a message and wait for the Admins to remove your IP from their ban list.