Thank you all for the replies and interesting discussion.
@PolyRob mentioned "it depends on where/when you purchased them." Very good point that I hadn't even thought about. The original tickets were from 2020 that I purchased at a discount from Undercover.
I sat down with large pot of coffee and some snacks and a fully charged phone at the ready and started the complicated exchange this weekend. Took me about 90 minutes on a couple of phone calls. Here's how it went.
I started with a call to Ticketing. Not too bad, about a 15 minute wait time. I stated I wanted to keep the same ticket (6 day park hopper plus) but change the start date to this April. I provided the original reservation number. That CM eventually found one of the two tickets and began the process but quickly ended with "Oh, this was purchased from a 3rd party. I'll have to transfer you to a supervisor."
And back on hold for another 15 minutes. Another CM picked up, asked how she could help. I explained that I was being transferred to a supervisor, etc. She replied that she was not a supervisor but, "let me see if I can take care of this." She located the original ticket. I told her there was another ticket that had been converted by Ticketing on the same day that I purchased them from a child to an adult ticket because I purchased the wrong one. She was able to track that ticket down too and was able to change the start date on both (so much for CM1's statement that this had to be done by a supervisor). To change the date on both to this April it was about $600 for both combined. A ~60% increase from the original cost just 4 years ago in 2020.
Then, I rang
DVC to convert these to Sorcerer Passes. The CM was able to do that, though very complicated because our daughter got married (name change) and she moved to a new home with her new family (address change). The DVC CMs are mighty quick to incorrectly jump on "She has to live at your address to be eligible for this pass," band wagon, when in fact she herself is on our DVC deed. I finally straightened out that CM and things proceeded. Another $400 roughly combined plus $200 combined to add the water parks and another $100 to add Memory Maker to one of them.
So, all in roughly $1,000 saved by using the value of the old tickets.