I did the same in the area I live (Edinburgh, Scotland) well worth doing, makes a big improvement to anyone doing reverse geo coding in those areas.

I actually used JOSM and did the changes as completely new ways and using the mapnik layer as a background. I decided this would be easier to work with as I expected others to refine the areas and later. But I guess if the area is distinctly defined by features then using these also makes sense.

I actually wonder is we need specific tagging for transient events. So for example the naive user would pick up the normal road, but a more sophisticated user could render the road as closed. In addition it could include an expected end time.

Yeah - still well worth visiting and getting a tracklog to check the positioning and the routes on and off.

Sounds totally disproportionate. I would be looking at filing an official complaint.

Definitely look they they didn't realise what they were doing. I would send a nice message and look at reverting/deleting the changes.