I know, I'll take the Retail W10 off my 1700 Ryzen and put it on my
Threadripper build next month in Sept.
And for only $20 vs $149 OEM, I'll put this $20 key on the Ryzen 1700.
Microsoft has tightened the screws on Windows Activation in one of the recent updates, if you do this you may end up permanently breaking the license you already have. The old Windows Vista/7/8 method of spitting out that eight-block hash and then phoning the automated service for a new hash has been deprecated.
If you want to skirt the hairy edge of legality but at least have a legit license key that won't raise any flags, search "Windows 10 Pro OEM 64" on eBay and then pick any high-rated seller that is offering sealed OEM/system builder packs for less than $50. So far I've found these copies to be legit. The seller might be violating their contract by reselling them, but at least you will get an envelope with a DVD and activation code that won't raise any red flags on a custom-built system, because it's being installed the way Microsoft intended.