I've booked a special (that includes resort credits) for a trip in July to CN. I want to add a day and possibly pay for an upgrade. Will this cause me to lose my current special or would it remain as is? Would I just incurr the upgrade fee and the extra night fee? I am assuming (I know - not a good idea) that the upgrade fee would be the current room price difference times the number of nights. If anyone has a past experience with this I would appreciate your help!

I forgot - part of the special was booking the room category we have currently booked.