I doubt it very much. The only way you could unfreeze an account would be if you could hack into the actual site to gain admin powers. Then you may be able to do it I suppose, but you'd be re-frozen again in no time and drop yourself into a whole heap of.. trouble.
yeah, pretty much it would take a pretty good hacker to get into neo systems, and make themselves admin, and unfreeze accounts
=X I dunnu. I really doubt it's even possible. I can't even imagine how many security codes and stuff Neopets has in place to stop that kinda thing. I'm sure people have tried before, but it must be almost impossible. I betcha not even all of TNT can have that much power.