We did something like this beginning of last year when DVC had a discount on the Premier AP. We already purchased WDW Premiums on the previous DVC discount so we had to give them our WDW AP's in exchange for the money value they held THEN paid the remaining balance on the DLR price of the DVC discounted Premier AP's.
Our only issue was the expiration dates. WDW's Premium expired Dec. 2014 but when DL sold us the Premier the expiration dates were for March 2015. (THEIR mistake) It was a bit of work to make the dates match up for the recent trip to WDW BUT they made the adjustments for us at no extra cost. So if we WERE to go back to WDW we have til March this year on Premier AP's!