It all depends on what type of Windows key you have. If it came with the PC, then it is locked to that motherboard. If it was purchased separately then you can move it to another pc. I bought a copy of Windows 7, which in turn I upgraded to Windows 10. When I built my new pc, I deactivated the key through my Microsoft account and reactivated on my new PC. You don't need a Windows 10 key, but some of the customisation features wont work until you have activated it.
Are you changing the OS drive ? If not then windows 10 is pretty tolerant of hardware changes even between Intel and AMD. The only time you absolutely need to reinstall is between 64 bit going down to 32 bit.
You might need to activate which you can online if you have original license key or via phone.