Fortunately, the premiere appeared to have a reverse psychology effect on crowding. Everyone assumed it would be packed... so fewer people showed up. Lines were very reasonable all day. Only Space Mountain and Splash Mountain occasionally breached 60 minutes at certain points, and I was able to easily use the walk-up line for Oga's Cantina.
Operational impacts due to the premiere were fairly negligible, for the most part. The Enchanted Tiki Room and Tropical Hideaway were closed all day to facilitate a pre-party area, but Dole Whips were still available at the stand. Jungle Cruise shut down from 4 to 7:30, and the two railroads - Casey Jr. and the main train - shut down early (with ample warning via app pop-ups). There were also no fireworks - only projections - but that was published well ahead of time, and they sent another pop-up notification to warn waiting guests. It definitely strained operations at times when the film's stars appeared - the Rock and Emily Blunt apparently insisted on coming out of Tropical Hideaway to greet waiting fans, which was honestly a nice touch. They tried to force guests to "walk through" that Adventureland artery (sort of like how they do for fireworks and Fantasmic), but most still stopped to watch and ignored the poor CMs. It honestly wasn't terribly much of an issue, and it relieved demand for Indiana Jones. (After catching a glimpse of the stars - again, surprisingly easy to do - we ducked into the queue and enjoyed a brisk walk to the loading station). All in all, hats off for a very smooth operation. Could've been way worse - though I wish they had published more of the impacts (aside from the fireworks pyro) ahead of time.