I agree that given the reduced schedule for F! (weekends only), the popularity of HalloweenTime, and that being UEA weekend, the packages are likely already fully booked. I would call to see if you get pixie dusted, but I would not count on it. Otherwise, I would keep checking as frequently as you can, be flexible, and hope that something opens up. As the PP said, I also heard them offering guests the chance to upgrade to the F! dining package at CO two weekends ago (but it sounded like only the 10:30 pm show was available). So it can happen, but you cannot count on getting a walk-up to CO or that upgrades will be available.