I no longer do that with running computers. Last time I tried it, a hard drive died.
power up and search for something called Never10
Yes, Never 10 was created by the great Steve Gibson of Spinrite fame:
https://www.grc.com/never10.htm
"Hiding" Windows 10-related Windows updates such as KB 3035583 worked for a while to block the upgrade, then in a substantial breach of ethics Microsoft started overriding the "hiding." So if you don't want 10, forget hiding updates, go with Never 10.
That said, while I am starting to hate Microsoft, I actually like Windows 10, except for its privacy violations. It has been perfectly stable, and has some nice new features.
To thwart at least some of Win 10's spyware activities, I like "Shut Up 10," from https://www.oo-software.com/en/shutup10. I say "some' because Microsoft's new OS is designed to phone home, and it can probably find ways to do so.
I no longer do that with running computers. Last time I tried it, a hard drive died.
Sorry to say, but that was a weak drive then. Sometimes you have no choice, like when the upgrade is progressing or initiated and the OS will not allow you to shutdown properly and no amount of clicking on your part will stop the process. Like on a laptop for instance when it is frozen sometimes the only option is to unplug the power pak and then remove the battery.