Just out of curiosity - if I have installed Windows 10 using one serial from earlier Windows(7/8/8.1/etc) and it got digitally entitled can I later change the Windows(7/8/8.1)/etc) serial key I used to a different one? Assuming both are legit and of exactly same type of distribution? In "Settings" tab there is an option to change product key, would putting Retail Windows 10 key there work? Also, would changing key affect existing Windows 10 installation?
If a system is digital entitled there should be no need to use any key on a future re-install because the system should be re-activated by the digital entitlement. But i don't know if the use of an earlier win 7/8.x key gets a hwid and will be linked to that key (i expect yes) or that the system gets the same digital entitlement as meant by HWID.