Hi Kathleen!
Generally speaking, the price of a
Walt Disney World package is comparable to purchasing your
Walt Disney World Resort hotel and
tickets separately. You can definitely book your Walt Disney World Resort hotel in advance and add the theme park tickets at a later date. Given that there isn't a price difference between the package and purchasing separately, you won't have to worry about applying a package rate when you add the tickets.
The exception is if you purchase a
special offer that includes both the resort hotel and theme park tickets. If you want to apply a special offer, after you've already booked your Walt Disney World Resort hotel, you can cancel your existing reservation and make a new one with the special offer applied.
I see that you are arriving in October, which is awesome!
Fall is my favorite time of year to visit Walt Disney World because of
Mickey's Not-so-Scary Halloween Party! This event is so much fun with trick or treating, Mickey's Boo to You Parade and Halloween decor.
I hope you have a magical vacation!
Magically,
Stacy