I like the commenter who said at last he had found a way to stop Windows 10 upgrades.
I think that I would want to block updates by keeping Win 10 off the WAN (well my first inclination would be to have something easily discoverable within the OS and to have it remain available (even the registry edit was taken away in an update if you had to install the latest version on a new build)I mean, they still have 9x blobs of code in Win 10 that cause issues of various severity and yet they couldn't keep that functionality? Come on) versus running a software build that is legacy, especially if it's anti-virus/malware etc.
Of course, a block like this would be reliant on MS for putting proper blocks in place. That's not always been the case (insider's branch getting deployed to everyone as a regular update and not just for "seekers").