Well. probably depends on your circumstances. If you have a package > then it might be harder? OR if you have a room only, or room only code > then it is usually cancelable up to 5 days.
But, once I was in a resort, and unhappy with it > we talked to guest services about a move and did in fact move the next day. Completely in the middle of our vacation. So, they are very willing to work with you.
I would say [even if your in a package] it doesn't hurt to call and ask. What is the worse they will say "no". Just call and ask.
I think that only applies if you go down in cost. We changed from POFQ to CR 3 days before our trip this past July and had no other charges other than the increased resort price. It was payable immediately since we had a package and were well within the 45 day window.