Can your ex change holiday visitation?

I'm not sure I understand why he wants to change the Christmas schedule after 6 years but presumably, you and he have a written agreement or court order spelling out who has Christmas eve and who has Christmas day ( and what time is the pick-up / drop off and where the exchange is to take place). Pull out your agreement/court order and read what you and he agreed up / court ordered - that is your starting place. If he says that he wants to change the arrangement, take a deep breath and ask him what changes he wants and why he wants those changes. You may disagree with him and there may not be any real reasoning behind his request but unless and until a new court order is put in place or a new agreement is entered changing the schedule, your current order/agreement controls the holiday schedule. But....if he files an application with the court, saying that he wants to change the current schedule, he has a right to do so and you have the right to oppose his application ( and to also address any other issues outstanding that you feel need to be addressed) and then either the court will rule on those issues or the court will send you and him to outside mediation ( if the court feels that there is a legitimate dispute between your positions) in an effort to peacefully resolve it. If mediation is unsuccessful, then the court will bring both of you back and rule on the request to change the holiday plan and enter an order as to who has Christmas eve and who has Christmas day or whether it rotates annually and what time is the pick-up/drop off.  One alternate suggestion is to hire a divorce lawyer as a mediator now and submit the issue to the lawyer. The lawyer can review both of your positions and even meet with both of you by zoom now and if resolved, enter a form of a consent order or amendment to your agreement detailing the change in the plan and it can be handled quickly and less expensiviely. In this setting, the lawyer is neutral and works with both of you and potentially can get the issue resolved before Christmas.