I tried to have the new promotion applied to the existing reservation and they would not do this and i received the following:-
Often, as in your case, you may find that you confirmed before a
particular promotional rate or offer is made available, however you
benefit from the abundance of resort availability, allowing you to
guarantee the location of your choice.
Regrettably, we will not be able to honour our new offer or pricing to
your current reservation. To take advantage of this current offer you
must cancel this reservation which would be subject to all applicable
fees and penalties as outlined in the Walt Disney Travel Company Booking
Terms and Conditions.
I did end up cancelling, losing the deposit and rebooking last year however want to avoid having to do this again. Any help would be appreciated.