I've taken apart older projection TVs in the past to clean the projectors/screens. Usually it's not that hard to do and done with care you should be able to do it. It needs to be done on a projection TV every few years anyway to remove buildup from the inside of the screens and the projector lenses. Not sure exactly how your TV differs in that regard from the older CRT projection TVs (arcade monitors that were just projection TVs with RGB in only) I've worked on.
Given the potential warranty violation, though, it may be worthwhile just to have it done by a pro. And be sure to keep the documentation of that as the manufacturer will require it if you need warranty repairs.
Dartful, asking them to pay for the repairs, if he's not a raging a-hole while doing so, shouldn't have any negative effect on the friendship. If it's a quality friendship they'd be offering to pay. I'd be insisting if my son did that.