the 6s has that special adhesive sealing once they've opened it up in that video.
so i was wondering what happens when screen changing is needed for example?
i don't suppose they can re-seal it as before, can they?
It's more of a sticky gasket than anything. They should be able to take care of something like that. They might also just replace it every time they do a repair since you could easily attach the gasket to the replacement screen and place it in. It might be harder to keep it intact during DIY repairs though.
It could be possible that when apple store do carry screen replacements that it will already have the sticky gasket on it, just have to remove the protective film before installing. But that would be my guess.