I've had mixed luck with them pulling inventory back. Last September I booked a studio at SS for 4 nights over Labor Day weekend. The morning of my check in, I saw that there were cash reservations available for Polynesian Villas. I called member services and got a great CM. I asked him if there was anyway to pull that cash inventory back & use points. He said to hold and he would call the resort. His tone and demeanor made it sound like he'd done this before and understood exactly what I was asking. 5 minutes later my SS points room was changed to the Polynesian Villas for a few extra points.
Fast forward to last week and I had a points ressie at BLT and saw that BWV had cash availability for the days I was going. I called the day before my check in and the CM sounded like I was asking to book the Castle Suite on points. She said that they NEVER do that. She then transferred me to a supervisor and she also said it NEVER happens. I told that it does happen, as I had it happened to me 4 months ago. She then looked at my reservation from September and was baffled by what she saw. She kept giving me different theories like I paid cash (ah, no) or that there must have been points availability (again, No). She was extremely nice and I never even remotely got angry or tried to seem like I was entitled to anything, I was just trying to understand the policy.....which she reiterated is it NEVER happens.
It's something in the future if there was a more desirable resort available for cash on my check-in date I would probably call in again and see if they could work some magic, but my expectations of it being successful would be pretty low.