Invariably, crew will dim the windows. Invariably too, you should be able to override this though you may face - in no particular order - crew trying to override your override, other passengers giving you evil look, the system being slow to respond or giving you various unappealing shades of grey, etc.

Personally, I'm not a big fan of the 787. The air quality is definitely better than on the 777/other old aircrafts, but it is not a particularly silent aircraft (350 and 380 are both much better on that front), and layout tends to feel a little bit cramped in most cabins (that is particularly the case in Y on the 788, but I do think that even the J cabin feels more cramped than other old CW layouts. Don't take me wrong, it is not horrible or anything, but just not among my favourites.