Is there a compelling reason why you would prefer a Dec UY over a Feb UY? Your UY is really only an issue if you have to cancel a trip. If you regularly go to WDW in Dec or Jan, then a Dec UY would be better than a Feb UY but it's not clear that it would be worth getting a completely separate master contract (vs. an add-on) just for that reason. You would be giving up the option of pooling your points to make a reservation and for banking purposes if you go with a new master contract.