In my experience, the crew probably *will* dim the entire cabin ... but they will probably *not* lock the controls.

I've seen all combinations, so I know it's possible for the crew to force the windows to stay dark - but in general, they simply pre-set it to a level. If you have the window seat, you will probably still be able to undim your own window. That was exactly the state when I flew AMS-YYZ on a 787 yesterday.