It's reasonable to have an option to disable this sort of thing. It would make a significant minority happy, and the existence of the option, implemented correctly, wouldn't likely really upset anyone.
We could call it something like turn off non-essential seasonal functionality. That's simultaneously professional sounding and silly-easter-eggish, so it's an appropriate name for a feature like this that resides on the border between them.
Named well and placed unobtrusively in the user's profile settings, the existence of the option shouldn't get on anybody's nerves too much.
I don't think this option should be enabled by default. If it's there, people who want it can use it.