We're going to get an email invite after March 6 with instructions. My guess is you'll have to register online and bring your printed ticket. If you have an annual pass through Costco or anywhere you need to make sure you connect your member ID number with your email address. I attended the Special Events Stuntshow Passholder Preview and that was how they handled it then. I assume it'll be the same with Hogsmeade, except we'll get more options for dates and times to register.
ah cool. did you get any +1s (i.e. if you had friends that weren't passholders but were willing to buy a day ticket?)