Presumably I would only ever switch if there was a problem with 2020 and a document that I needed to compile. I keep the current and one previous texlive installation, just in case. I've never needed it, but was curious what I'd need to do if I did.
I'm not so much after a utility, I followed `which lualatex` and followed the links, and found the .rtf file which described `texdist` (which I've just noticed dates to 2014, whichis when I got the machine.)