From this article, sounds like it's best to perform any hardware upgrades you have in mind BEFORE upgrading the software to Win10.
Otherwise, you risk losing your license, and MIGHT have to buy another.
Microsoft quietly rewrites its activation rules for Windows 10
Windows activation is alive and well in Windows 10. Microsoft doesn't like to talk about the inner workings of its anti-piracy software, but it's clear from testing that Windows 10 included a major change in the way activation works.
By Ed Bott
Windows product keys are almost (but not quite) a thing of the past.
With Windows 10, Microsoft has rewritten the rules for how it performs product activation on retail upgrades of Windows, including the free upgrades available for a year beginning on July 29, 2015. The net result is that clean installs will be much easier--but only after you get past the first one.
OEM activation hasn't changed, nor have the procedures for activating volume license copies. But the massive Get Windows 10 upgrade push means that for the near future at least those retail upgrade scenarios are very important.
The biggest change of all is that the Windows 10 activation status for a device is stored online. After you successfully activate Windows 10 for the first time, that device will activate automatically in the future, with no product key required.
That's a huge change from previous versions of Windows, which required a product key for every installation. And it's potentially an unwelcome surprise for anyone who tries to do a clean install of Windows 10 without understanding the new activation landscape.
Microsoft is characteristically shy about discussing the details of activation. That's understandable, because every detail the company provides about its anti-piracy measures offers information that its attackers can use.
But it's also frustrating, because Microsoft's customers who use Windows don't want to have to think about activation. The Windows PC you paid for, and the free upgrade you spent time installing, should just work.
I've had some way-off-the-record discussions with people who know a few things about the subject, and I've also done my own testing for the two weeks since Windows 10 was released to the public. Here's what I've learned.
Your Windows 10 license is stored online and linked to your device.
For more than a decade, one of the keys that Microsoft's activation servers have relied on is a unique ID, which is based on a hash of your hardware. That hash is reportedly not reversible and not tied to any other Microsoft services. So although it defines your device, it doesn't identify you.
Here's how that ID works with Windows 7 or Windows 8:
When you activate for the first time, that hashed value (let's call it your installation ID) is recorded in the activation database alongside the product key you entered with the installation. Later, when you reinstall the same edition of Windows on the same hardware, with the same product key, it's activated automatically. (Conversely, if you try to use that product key on a different machine with a different hardware ID, you'll probably be denied activation.)
Windows 10 goes one very large step further.
When you upgrade from Windows 7 or Windows 8.1, the Windows 10 setup program checks your current activation status and reports the result to the activation servers. If you're "genuine" (that is, properly activated), the Windows activation server generates a Windows 10 license certificate (Microsoft calls it a "digital entitlement") and stores it in conjunction with your installation ID and the version you just activated (Home or Pro).
It didn't need a product key to do that activation. All it needed was the proof from the Software Licensing Manager utility that your underlying activation was legit.
You can now wipe that hard disk completely, boot from Windows 10 installation media, and install a squeaky clean copy.
The Setup program asks you to enter a product key, but in a major change from Windows 8 and 8.1, it allows you to skip entering that key.
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The one exception is a motherboard replacement, which will inevitably cause the Software Licensing Management utility to recognize the device as a new PC and require reactivation <READ YOUR WIN10 LICENSE WILL NO LONGER FUNCTION>, typically over the phone. A motherboard upgrade, even if you reuse storage, video, memory, and a case, is considered a new PC. In that case, if the underlying Windows license is from a retail copy, that license can be transferred. If you are upgrading (and not replacing) a motherboard on an OEM PC that was sold with Windows preinstalled, the license agreement prevents the license from being transferred.
Story Continues
Note: The comments section grew QUICKLY with a few dissatisfied users, and many questions.
Seems the biggest concern was, "If I swap out a hard drive, will by license become VOID?"
A few commenters were in Tier 2 Support H3LL trying to resolve the issue (FAILED activation after re-install).
Service Pack 1 anyone?