Earlier quoted context omitted.
In this case, every giving would be stealing. If I gave you something, you didn't steal it from me. Likewise, if I gave you the right to impersonate me in particular circumstances, it's not a criminal offense if you do.
It depends on where you are in the world, but in most places in the civilized world, criminal law does not work that way. If something is illegal, we cannot sign a contract that says it's ok between you and me, and magically make it legal. E.g. if I kill someone, the state will prosecute me for murder, regardless of whether or not that guy and I signed a contract that said it was fine. If impersonating someone is a c…
A contract can establish consent.
E.g. if I go into your house without permission and take stuff, then it is theft. If I have a contract saying that I have permission to go into your house and take stuff, then it is not.
I have not contracted my away from something illegal. The contract has established consent, which meant the criteria that otherwise would have made my actions criminal are not fulfilled.
> If impersonating someone is a criminal offense in a particular jurisdiction, then -- assuming that jurisdiction has a sane criminal code -- there is no way to make it legal through a contract.
That depends whether or not the criteria that needs to be met for it to be a crime requires lack of consent. If it requires lack of consent, then a contract can document that the consent has been given.
All jurisdictions I'm aware of (not a lawyer) have the concept of agents that may act on your behalf with consent. To what extent such agents can act using your name (with consent) vs. using their own name but on your behalf, varies greatly.
E.g. some places your agents (say a PA) will sign letters "[agents name] for and on behalf of [your name]" or similar, while other places they will use a signature stamp with your signature, or do "p.p. [their signature] [your printed name]" (the p.p. stands for "per procurationem"). Many other variations are in use, and how obvious signs there are that a document was not personally signed by the person the letter is from varies greatly.