Artist tags rename/move discussion

I've noticed that several artist entries were renamed and posts moved to new tags (not aliased but moved). This isn't anything new and not necessarily a problem by itself. But the fact that it was done without any notice or discussion may cause some confusion, so I though that we should decide when this is acceptable and how it should be done properly.

To give some examples, see history of artist #52992, artist #4878 (also see discussion in topic #9294), artist #28305.

I do think that well established artists, like artist #28305 (was previously tagged as "mogu"), should not be moved without some prior notice/discussion. This breaks user subscriptions and can leave users wondering what has happened because it's not always easy to find new artist tag.
Even if the move is seemingly painless it's still better to make others aware of it (basically, I'm agreeing with what NWF Renim has said in topic #9294). Perhaps we should have a separate thread for discussion and as a log of all such cases.

For, say, under ~30 posts I'm okay with someone doing a move if they put a notice in the old tag's wiki pointing to the new one.

Anything between ~30 and ~70 would be aliased unless the old tag was ambiguous.

Anything over ~70 tags I'll tend to alias even if the old tag was fairly ambiguous, because that's a sizable number for an artist.

Note: numbers not set in stone, and totally subject to my whims at the time I hit the artist alias thread.