@DaveF, I live in a pragmatic world where I'm concerned about actually getting stuff done. No amount of whinging on a changeset comment will change the fact that some communities and individuals are heavy on rule-lawyering and perfectionism. With this reality in mind, any edit that will get reverted is a waste of everyone's time. Despite what you seem to imply above, the US is one of the more amenable places to bulk and mechanical editing. However, it still requires a base understanding of community expectations.

I similarly bulk-edited 30,000 or so riverbank tags in the US, with community support and a good understanding of where the data came from and how it came to be. So I am absolutely a fan of bulk and mechanical

See:
https://wiki.openstreetmap.org/wiki/WikiProject_Waterways/River_modernization

I largely agree with Carnildo's description of reservoirs tagged from the GNIS import. Tens of thousands of farmer's cow ponds in North America are tagged as reservoirs, and the presence of the old tag gives us something to go off of in sorting these out into "reservoir" and "not reservoir". But, if you've never looked at the data or talked to people who map these areas, you'd never know about them. Merely upgrading the tag makes finding and fixing problem data harder.

Meanwhile, after a brief discussion on the Czech mailing list, every landuse=reservoir in the Czech Republic was upgraded to the new tagging. The Czech mappers understood that no underlying data issue made this problematic.

In the Czech case, it was a quick note on their mailing list, and then the edit a few days later.  In the riverbank case in the US, it was quick notes on Slack once it was clear there was no opposition. Bulk editing doesn't need to be excessively process-driven, but it does need a minimum level of understanding of the data that's being edited and at least a courtesy interaction with the community involved.