Hey, Heather and welcome to the Disney Parks Moms Panel. Winter time at Walt Disney World Resort is so magical. All the theme parks put up giant trees over 60-feet tall, wreaths, special holiday lighting and of course, the delicious treats baked my Mickey and the gang.
I have not seen two Special Ticket Events on the same night excluding dessert events related to fireworks spectaculars so I would not worry about conflicting programs. If, however, there is another event, such as
Disney After Hours, that takes place at the same time as
Mickey's Very Merry Christmas Party and you want to attend it, then do the following. Contact a Cast Member (Disney speak for employee) at (407) 939-5277 and explain to them your situation. My cousin had an issue with a hard ticket event that needed to be changed, the Cast Member looked for another night that would work for them and switched the date. While this should not be expected, know that Cast Members do their best to "bibbidi bobbidi boo" help so you have an enchanted vacation.
Disney Dad Tip: While visiting Walt Disney World Resort make sure to visit
Disney Springs during the holidays and see the Christmas Tree Trail. Each tree is perfectly themed with a variety of Disney experiences and movies. I love the Haunted Mansion and Toy Story trees.
Heather, enjoy making many Magical Memories.
~Jason