Yes,
but consent is not something that can be universally declared in a credible manner. There are things that remain illegal even after you have consented to them. For instance, having sex with someone below the age of consent is illegal even if they have consented to it (the idea being, of course, that they may be coerced into expressing that consent).
> 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.
They do, but things are not as simple as "can act on your behalf with consent". Around here, for instance (but I'm in Europe), they can only act on your behalf if:
a) You have explicitly given them consent to act on your behalf in that specific situation (i.e. you told them "you can go to the bank on this date and cash in this much in my name"), or if you have explicitly given them consent to act on your behalf with that particular party and for a specified period of time (i.e. you can go to this bank and do anything in my name for this period of time), and
b) The contract that states this has been validated by a notary and recorded by authorities, and
c) The party that they are acting on your behalf with knows about this, has been explicitly informed that they are acting on your behalf, and agrees to work with them under these conditions.
If they fail to do any of these, it's flat-out illegal. I think this is covered under civil law here, though, so it can be voided by a contract -- but the idea is that consent is not as trivial as signing a sheet of paper that says yeah, do whatever you want. It's bound by specific terms, too, the breach of which makes the whole thing illegal, even if on the whole the operation was consensual (i.e. if an agent, with my consent, goes to the bank to cash in a deposit, but does not explicitly inform the cashier that they are acting on my behalf so that they record the transaction accordingly (i.e. done by X on behalf of NotALaser), he's breaking the law).
(Edit: or, to make it clearer: he can represent me, but he cannot claim he's me. He has to explicitly inform the other party that he's acting on my behalf, declare his identity and present the proper authorization etc.)