nope. you are not locked in.
it's preferred to make a reservation at your home resort at 11 months out and then, if you want, call exactly when the 7 month window opens to try to switch resorts.
no penalties or anything, but if you banked or borrowed pts to make the 1st reservation, be aware that those pts cannot be put back in their original use year.
(but naturally, you are limited by availability, so if the new resort is booked up - which can happen at any point - you would be out of luck.)