I sometimes use push pins ever so gently pressed into the ceiling...99% of the time, even if the location changes, the hole for the fixture or the trim ring will cover that tiny little hole.
Of course, BEFORE putting these little pin holes in the ceiling I get the HO's approval to do it ~ also works to confirm the fixture locations with the HO. They can see the entire layout before an actual hole is made.
For the "attic crawl"....a couple of pieces of cut plywood...2x3' works well, which leaves a little extra piece for placing tools and the flashlight.
Of course, BEFORE putting these little pin holes in the ceiling I get the HO's approval to do it ~ also works to confirm the fixture locations with the HO. They can see the entire layout before an actual hole is made.
For the "attic crawl"....a couple of pieces of cut plywood...2x3' works well, which leaves a little extra piece for placing tools and the flashlight.