Yep! If you book your Disney hotel room at full price and a discount you want to take advantage of is released at a later date, you can actually modify your reservation. There's no guarantee that the hotel or room type you booked will be included in the discount, but if your plans are flexible, you can switch things around to take advantage of the cost savings.
If you make the reservation yourself, you can do this through Disney's website or by giving them a call. If you book through a travel agent, you'll want to contact them so they can make the change for you.