Cloning i don't know. But as for Windows 10. you can download Win ISO image from official website and use rufus to make a bootable usb. Also regarding the key. you dont to copy it. the Windows 10 binds it with your Microsoft account if u login in Win 10.
After clean install of win10 just use same Microsoft Account to login and it will automatically gets registered. Win 10 key is bind to your CPU and Main board. if u change any of these. Then you will need new Key for windows.
You're not totally correct about the binding because there are two licenses of the Windows one is ''OEM'' & one is ''Retail'' the OEM license is cheaper than Retail license but the OEM is stuck to the motherboard where as Retail can be deleted from one PC & installed onto another but it can be installed onto one pc at a time & these Brands such as Dell , Hp , Acer etc all buy OEM licenses of Windows in bulk so they even get it more cheaper With 7 and earlier, you weren't allowed to use an OEM license yourself (though lots of people still did/do). That changed with 8, and you are allowed to. Nothing wrong with it, other than that you won't get any help from MS. & but since I've a Custom pc & not a pre built one & I've the Retail license so it's not stuck onto the motherboard
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& as far as for cloning the Windows I done some research about it & the answer is yes it can be done through a cloning software such as EaseUS or Aomei backupper etc I'll need to connect the new HDD > use it as a slave drive > then make partitions in it > then clone the Windows onto one of the partition > then disconnect the old HDDs > then boot the system with only the new HDD & the partition where I cloned the Operating system will automatically be renamed to C drive or will I need to do that manually by going into Disk management?? & just in case I should make a recovery repair disk just in case if anything goes wrong