There are a limited number of rooms allotted to FD and you can add it as long as the room type you originally book is included in the promotion. If not, you'll have to cancel your current reservation and rebook. FD is always part of a package deal in which you must purchase a minimum number of park tickets (last year you also had to purchase the park hopper or water park option) and pay full rack rate for the room. Also be aware that it's the Quick Service dining plan included at the Value resorts. You can get the regular DP if you want it, by paying the difference between the two plans.