1.
There is no "deactivation". You may see some posts relating to a command line function that purports to 'deactivate'. so you can use it on new hardware.
This actually does little. It tells this PC it no longer has an OS license. It does NOT phone home and tell the activation servers that this particular license is unused and available to use on a different PC.
For Windows 10, and the recent 1607 release, they have changed the licensing.
You can link a license to a MS account, rather than to specific hardware.
Read here:
https://support.microsoft.com/en-us/help/20530/windows-10-reactivating-after-hardware-change
Reactivating Windows 10 after a hardware change
"In Windows 10 (Version 1607 or later), you can link your Microsoft account to the Windows 10 digital license on your device. This can help you reactivate Windows using the Activation troubleshooter if you make a significant hardware change later, such as replacing the motherboard."
Previously, an OEM license was tied to a specific, original motherboard. The only way to use that specific license was to beg Microsoft. Sometimes yes, sometimes no.
A Retail license is usable on different hardware. Usually it activated no problem, sometimes you had to call and ask.
As always...1 license, 1 PC at a time.
Also as always...Kinguin is a no-go.