Noted.  Had assumed the risk was mainly to my hoods, not game files, but now I know so I'll be a bit more circumspect about using it.  Wish I knew, well actually wish you knew, what could've caused it to react so differently this time.

I've used the batbox to rename townies often, sometimes 'change first name' doesn't take after a 'copy to last' or having changed another sim's name unless I unpause the game, but that just means that nothing happens.

Playing a new uberhood in a game with maybe a third of the cc in my main game folder, so far twice the renaming has gone...wrong.  The cancel error didn't pop up for me to enter name, it went straight to the 'new baby' screen, twins both times, and has the name of an NPC object at the top and a random townie at the bottom.  The first time it was Bigfoot but I didn't realize the problem because I forgot there's no instantiated Bigfoot copy in this hood.  This last time it was Crumplebottom.  There's no way to cancel the naming, you can only 'ok' it and, when I checked, indeed my objects.package had a new date and filesize.  Luckily I had a copy that I've now made read-only, so no need to re-install/re-patch but seems like a VBT that it keeps choosing NPC objects that shouln't be overwritten when it errors.