Business Ethics 101 would suggest that the buyer of the 2010 be informed of the situation and the "married" tuner be part of the sale or offered as a deal "sweetener" or for additional funds. NOT providing this information could actually void a sale and possibly place the seller in some legal jeopardy, especially if the seller is a licensed dealer. If the buyer is informed, and does not want the part, he needs to sign a waiver. That said, if it were me, the part is an integral part of the OS and would be included.
Regarding Charles question, stock maps are easily "flashed" to original by any Harley dealer, but that would only make sense if the bike was returned to original condition. But ekim's question is a good one, although to remain consistent, I would say (as the seller) the tuner goes with the bike and it would be ekim's responsibility to buy a new PV unit for the new bike and his wife's.
We all have bought and sold stuff, I think we can agree that "honesty and fairness" are things we all expect in a deal for something we are buying. The guy we are selling something to, deserves the same.
OWL