You will loose your reservations upon upgrading.
Option 1: Check the availability calendar for your Magic Key choice. If there are reservations available for your stay, you can risk upgrading by immediately re-booking reservations after getting your Key. Remember there is a limit depending on the Magic Key type!
Option 2: On the last day of your ticket (during operational hours), you can upgrade on the App AFTER entering the gates. You CANNOT renter the park day of upgrading, so don’t leave!
Option 3: If you leave the DLR *before* the park/ticket booths close on your *last* day, upgrade at the ticket booth, and go home!
Simply, you won’t be able to take advantage of Magic Key discounts and perks until your next visit (unless you take the risky option 1 path!).