If you already used your code, then it's tied to the accounts you used it with. If you're lucky, you'll receive the email with a code like you're hoping and be able to use it on that. As far as early access; the previous testers received emblems and the like, but no actual gameplay element that can have an impact on actual gameplay (so no weapons/armor/abilities/etc); most likely D2's Beta is going to be the same. Do note that if you use a new account in D2, that any benefits for being a D1 veteran (if any) will not carry over to that new account.