I've been back and forth on this with UT, because we want to add a day...Ive been given some conflicting information via chat and email but just spoke to someone who was very helpful and walked me through it.
- you can add a day at guest services BEFORE entering the first park
-you can buy a new ticket from them ( with the added day), then give them the order number and they will refund 100%, no fee.
-you can go to
MDE, tickets, then "change ticket". Its on the left under the name- NOT the drop down "reassign ticket" option.
I didn't proceed because I want to first try to figure out how much it will cost to do this. I'll have to call WDW I guess?
I know this may not be helpful as far as an AP, but wanted to share in case.