Once I had my special booked with the disney visa I was able to go into the reservation online and change the resort and kept the disney visa Rate. If you are moving from one special offer
to another you will have to call. Don't think you can combine offers.
It isn't technically a special offer...it was a standard rate room with no discounts. There is a note in your account that you get the gift card, and it is combinable with any discounts. But if I try to do the change reservation link, it only offers the gift of magic offer, not the disney visa, and I am not sure how to get that to pull up.