I've been trying to do this since the beginning of August. I need to add a date to the end of my trip Sept 24-28 but there are no rooms available. I can book a room only for the night but I can't add on to my FD package. I've been calling almost every day now. The lovely CM today told me that even if someone cancels with the package the room goes back as a regular room and not to available package. I even had them try at different resorts, which would be an upgrade, but nope nothing available.