Hi @Steven1834
Two aspects that you cannot change per season are the way one books (instant or request) and the cancellation policy. These have to be chosen and set for the listing calendar as a whole.
In your case you may want to keep the cancellation policy strict while December is inside the booking window (unfortunately the policy will then apply to other bookable months also, but you can grant refunds from your side if someone cancels).
When December is not bookable (for example, when January starts and your window is 6 months), you can relax the cancellation policy to attract more bookings.
It'll take some concentration and effort!