either the boat is USCG registered or california registered.
if its california registered, you could just transfer it at the DMV and they don't care about your citizenship
if its USCG registration, I think you could register in California and cancel the USCG registration.
there is nothing in the DMV rules that limits you to the size of boat you can register.
I know that for a lot of countries state registration of a boat is problematic, but I would think it would not be for mexico. find out and you could have a solution