If you have Christmas Party tickets on a separate
MDE that doesn't have a resort reservation, just those tickets, you will not have magic bands for the party tickets.
If you have magic bands from a previous trip, you may be able to have them taken off the original MDE and placed on the new one with party tickets. Again, I am not 100% sure that you would be able to transfer the magic bands and if it can be done, how the heck to go about doing it. You could also buy new magic bands on
disneystore.com.
That seems like it would be quite a hassle to put the party tickets on magic bands. You could just use the party tickets at the FP+ returns, just scan them like you would the magic band.
This would probably be your best option if you want to take advantage of getting FP+ on your party tickets and park tickets. Like PP mentioned, you would have to wait until 30 days out to reserve FP on the party tickets because it would not be tied into a resort stay.
If someone else has more to add, please do so.