Hi Emelia!
Thanks for your question. Of all the special events that
Disney hosts annually,
Mickey's Very Merry Christmas Party is by far the favorite event for me and my family. Christmastime magic overfloweth at
Mickey's Very Merry Christmas Party! From the Once Upon a Christmastime Parade to the (new)
Minnie's Wonderful Christmastime Fireworks, there's no place I'd rather be come Christmastime than
Disney World!
Unfortunately, once you've secured your ticket to
Mickey's Very Merry Christmas Party for a particular date, that date cannot be changed or refunded. My educated guess is with the thousands of guests that attend the event annually, Disney needs to ensure they can accommodate all guests for the night of their scheduled event. If dates were constantly in flux, I could envision logistical challenges they'd be faced with in terms of crowd size, staffing, and park capacity.
Perhaps, if looking at it from an upside perspective, you'll have a special event to very much look forward to two days later when you touch down on December 13th!
Hope you and family have the merriest of times at Disney World!
Terry