I just upgraded my mobo, memory, and cpu. And I then did a clean install of Win10 Home x64. I skipped the activation until I was all installed. Then the nightmare started. Well, not nightmare, but it just did not work.
At first it said my Windows 7 key was 'blocked'. So, I finally got on chat with MS Support, and after about 2 hours and a new big windows updated they said it should now accept my key after the reboot. Bye.. So they were done with me. And it did not work.
Luckily, Raj called back about a half hour later to see if it worked. I told him no.. Now it says that my key is 'in use' on another computer. So, he tried for another half hour. He brought in his manager I think and then they finally gave up and just gave me a brand new Win 10 Home key. Now I'm fine.
So, it is supposed to work. And it probably will for most people. But my Windows 7 key had issues. Even when I used it 6 years ago to installed. (I needed help from MS Support then as well..)
PS: MS Support had desktop control of my computer most of the time. I normally don't trust people that I do not know doing that. So after they were all done, and I had the new key. I re-installed Windows 10 from scratch. A new clean install with that new key and it worked fine.