jpdx,

I don't know about the MCO option, but just a few days ago I tried to do what you asked about originally. I had a reservation for just myself which I needed to move, as well as add my daugher to the PNR (so we could both get the Platinum upgrade). It wasn't possible to apply the credit from the original ticket to the new reservation, because the rules require that the new reservation is made for the same person(s). Therefore, I had to buy a new ticket and save the credit for later.

- Martin