Not sure why they would continue to wear costumes in Ten Forward for a promotion, considering that they were holding the celebrations for said promotion on the holodeck.The holodeck of the Enterprise-E (in First Contact) didn't seem to require a costume change (I believe it was RLM that had alot of questions on what Lily was wearing or not in that scene), so it's possible that this "update" in software was applied to the Enterprise-D late in its voyage.
Now, of course, there is the question of Generations a year later, which had the crew all dress up in 18th century period costumes, outside of the holodeck, but maybe the costume party was going to continue in Ten Forward or something and that's why they replicated those crazy outfits.
I have no explanation for Riker and Troi's appearance, but, you know, they're actors. Just like we shouldn't (necessarily) explain that Ishka or Tora Ziyal had plastic surgery a couple times to look like different people, we shouldn't need to come up with some convoluted reason why Riker and Troi looked ten years older on the holodeck (and in Ten Forward) during the Pegasus incident. Jonathan Frakes and Marina Sirtis don't look exactly like Will Riker and Deanna Troi. They're just approximations (as are their occasional stunt and body doubles), and the "real" Riker and Troi didn't age rapidly during that event.
Yes, they are actors, on a fictional tv show, and are doing an approximation of an episode that was aired 15 years earlier. But I don’t see why it cannot be looked at the way I laid it out, once the holodeck upgrades are taken into account. It just makes the in-universe storytelling look more consistent.