Speaking of changes, I know park hours have been wonky lately, but the park hours for 6/10 have currently shifted.
Disneyland: 8:00 a.m. to 8:00 p.m.
Magical - Disney's Nighttime Fireworks Spectacular
The Skies above Disneyland Park
8:40 p.m.
DCA: 9:00 a.m. to 5:00 p.m.
If it weren't it being the day of the WoC media event, I'd say the change definitely won't stick. But there are a lot more logistics here than a regular grad nite (seeing as they sold tickets for an exclusive event at DCA and last I heard are planning to block off teens from the whole Paradise Pier area, meaning that some of the best thrill and other rides are inaccessible). So I can imagine them wanting to clear out the teens earlier for the media event, and get them into Disneyland earlier for the same reason.
Though frankly if Disneyland closes at 8 PM but fireworks still run at 8:40 PM, that would mean that they'd start closing off the park except maybe the hub area, the castle area, and Main Street at 8 PM. (They usually close Main Street/etc. an hour later than the park so that's not impossible.)
But that would also mean that the vast majority of the folks who visited the park would probably be watching fireworks, and so the crowds would still be in the park until probably 9:30 PM. The difference would be that by 9:30 PM all the rides would be cleared out, etc. because no one could run from Fireworks to Indy at 9 PM, for instance, as I assume they might try on a normal grad nite.
Or they might have forgotten to remove fireworks from the schedule.

Since the hours they listed may not even be right, I figure it's hard to say?