Yes that's Right. When I installed my 3 ax battery's I did use jump-cables from one of an extra battery. I did NOT brake a +12v circuit to a van.Any little 12 volt battery (even two 6 volt lantern batteries in series)attached with jumpers (short wires with alligator clips) to the battery cables will keep all volatile memory intact while you make battery changes and modifications.
I bought my van used and the owners manual wasnt there so I have no clue what my code is. I'll ask the dealer as you suggested.My UC3 has 2359, and I am willing for you all to know, but it is a joke because no one is going to steal my radio! I have needed it twice when I disconnected it for the swivels and then for the new swivel.