Thank you for the input. You're right about the bulk edit guideline, and about the data now being part of OSM.

Since I've been (almost) the sole editor of this region for quite a while, including the buildings, I felt at liberty doing this. But it should have been discussed first nevertheless.

The inaccurate buildings a mild nuisance when I'm adding more accurate data that doesn't fit them, but since I have no particularly strong opinion on this , I'll simply perform revert. Does anybody have a problem with that?