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You could just pull the outlets and plates and put in speaker plates with black and red posts. Then choose which wire is going to be your positive (white or black) and make sure they are all the same at each outlet, junction etc.
I guess I would ask what you plan to run from the 12v system? Personally I would keep the system at 110v and just feed it with an inverter and battery. But even if you decided you want 12v, certainly no need to rewire everything. Wire is wire, just change your "outlets" the speaker terminals or cig lighter ends or whatever.