Yes, if the discounts are offered later, you can have them applied.
I had booked our February 2013 in early August 2012 for a package stay which includes room, dining plan and park tickets.
The discounts for our time period weren't offered until October - it was actually a play, stay, dine offer and not free dining as in previous years. I called and they applied that discount to my existing reservation and gave me my new balance due and amount saved. The Play, Stay and Dine offer could be applied to packages and replaced the Free Dining, at least for that time of year. It was a substantial savings though - almost as good as free dining.
Yes, if FD is offered you can have it applied to your current reservation IF the resort/room type you already have booked is available under the FD promo. There has to be availability under that discount in order to have it applied. Sometimes you have to be flexible with your resort/room type as having a reservation in place does not guarantee a discount can be applied.