Couldn't someone write an extension or something similar that would let a sysop rename a category using ajax?
- get the category members from the api
- for each, retrieve the wikitext, switch the old category name for new, get edittoken, save page
- mark all the edits as bot, or if you wanted to get fancy, make a new log for it
Good to see you there Blue, how're you doing? Nice Christmas and New Year?