Not possible, I'm afraid (unless it's the exact same model of motherboard. Many different things that could/would change with a different model and make Windows not boot). Even with the exact same model, the serial number would be different, so it would fail validation.
A method I saw on the internet somewhere was to use sysprep to return the computer to "out of the box" state (but it still keeps all the files, and I think settings.
Will try that possibly, not sure I want to yet or not.
Is certainly possible, like any 'new' install you'll need to install ALL of the new drivers i.e. Chipset, SATA, NIC, etc then (re)activate Windows which 'might' require a call to Microsoft -- if everything else is unchanged then you might get away with online (re)activativation Windows. This depends on your version of Windows and the pre-installation driver requirements (if any).
Note: IF the OLD MOBO was OEM e.g. (HP, Dell, GW, etc) then you don't have a FULL version of Windows and/or the complete driver library installed. So you typically cannot in that situation 'pop-in' a NEW MOBO.
It 'is' best to backup ALL documents and a clean install of Windows.