When Ben releases a Registration System,Will all of the people that got banned in the Global Blacklist will be lifted or not?

That would be decided when it happened - would require an admin talk with bcoolface.
I don't know when he's thinking of even adding a registration system..

Personally I'm interested in how the next update will affect the GBL, but if there's a registration system I'd side with removing some of the bans, if not most.

Another question: Will the accounts be linked to our forum accounts?

That's a technical question based on a feature that is not really being designed yet.. who knows?

I don't want someone to steal the name frosty and give me a bad rep.
Imagine if someone steals your name?

I imagine there would probably some partial way of preventing that.
Hypothetically, forum accounts could be turned into game accounts I suppose, but again.. this is a theoretical feature for the time being.