Just got back today from our Thanksgiving trip. The short answer is that yes! If you booked tickets prior to the October 16th change to specific date tickets they can be activated early. If you purchase "variable" date tickets after October 16th as part of a package they can also be activated early - I guess these are tickets that could be used anytime and not date specific. You really need to go to guest services to do this. I attempted to do this on the night we arrived and were staying offsite. We had Thanksgiving dinner at 1900 Park Fare and I visited the concierge at the Grand Floridian to attempt it. Let's just say she got ahead of herself and canceled fast passes that I had made. luckily it was for Sunday and my plan was to cancel these anyway and grab what I could for Saturday ( a crowd level 10 at MK). I went to GS at Disney Springs on Friday and after being deleted off the waiting list due to a glitch and waiting a bit longer than I should have not only were my tickets activated early, I managed to make the fast passes I expected to get at almost the expected times (Buzz, HM, and Pooh) but, I was also generously provided 3 multi experience fast passes for our family so we were able to walk on 7D, Space, and Splash on a Thanksgiving weekend.