you realize that you must be at WDW to get your tickets changed - so forget the fast pass getting them online - unless you arrive and don't go in the parks that first day - but you must go to the parks (not Disney Springs) to get the tickets changed. So I might wait to go to the parks for your next trip and just do the resorts this one. I might even consider buying new tickets for this time to do what you want to do.
I love Pop - but Pop crowded and it will be - might be hard.
I called and they said to email images of tix (back and front) and receipt and they would have it sorted in 7-10 days.
