Follow-up: do the water change no less than 24, ideally about 48 hours before you leave, that way you have some time to test parameters again and make any minor corrections if needed, but never do anything drastic. Better salinity be a little low for a few days than to raise it quickly, for example, as long as it isn't too far out of range to be safe.
Dialing the lights back is an easy one: corals and fish get cloudy conditions all the time in the wild, even in the sunniest of reefs. What we do in our tanks, with perfectly reliable lighting 7 days a week 365 days a year is patently unnatural, and except maybe in rare cases with certain corals, they can all stand a few days of lower light, blues and whites (or even just whites) only, simulating cloudy or storm conditions, etc.
Just keep in mind to bring the photoperiod and/or intensity back up gently afterward so as to minimize stress on your photosynthetics.
Kinda like with the aforementioned salinity (as I myself only recently learned), most things will handle a drop to a low condition much more readily than a spike to a high.