I'm not sure how to explain it any better than I did in my post, but I happen to have a recording of what I'm talking about; the recording will expire in the next 4 days
you'll find some examples of what I'm talking about around and after the 4:46.00 mark; some people were abusing this character-swapping, which I'd remarked about during the recording:
the addons used, in total, were robo-hood, input viewer, and my level pack, with no other addons
I was using the client found in this thread:
https://mb.srb2.org/threads/leavebug-anti-crash-hack.33071/
again, the players swapping skins when they weren't supposed to were using v2.5 of TSoURDt3rd, though iirc, one or more of them updated to 2.6 during the stream