Hi
Hmmm, I don't know why not, it didn't ask me for any registration number at all and I dual booted it on my computer.
So I don't know why having it installed would be using your Windows 8 serial number.
They didn't say anything about this acting as an upgrade and I think you could install it on anything.
I don't think you even have to have Windows 8 installed on your computer to install it.
But you might be better off downloading the .ISO file and doing it as a clean install on your computer in a dual boot setup.
If you upgrade from 8 it might consider it an upgrade and retain the number.
Once it's running change the boot menu to boot only to Windows 10, once it's doing that for sure, remove Windows 8.1 and install it on the other computer.
They would want you to deactivate it from the computer you are removing it from before reinstalling is my guess.
This is all conjecture, on my part, I have no real experience that would prove this to be true.
Mike