Hi Monkey pie
On the face, I'd say if you're using the same stone it will be difficult- if not impossible.
But if you can show a picture I might be able to give a more advised answer
We've done it, but not using the same stone- because the amount of room on top changes.
My ering was turned from prong to bezel, however the same stone was not used (like in RD's example). A slightly smaller center stone was needed when the ring was changed to a bezel.
Oh yes, I knew I didn't want to use the same center stone. It was just sort of a curiosity question because I saw a ring I liked, but I want only bezels now with a 6 month old that gets scratched easily, you know? All the more reason for a new ring