When you have Windows 10 already installed in your SSD/HDD you just need to connect it with a SATA cable to the mainboard and don't need to reinstall Windows again, however you probably need to update your BIOS since you are getting a new mainboard and download it from the manufacturer's website (pc will still work fin but it's simply always recommended to have all your drivers for your hardware up to date.
If changing to another mainboard Windows should normally boot up as long as it's already installed in your SSD/HDD however I do not know whether you have to activate Windows again, since to this day I have not activated my Windows 10/buyed a key license.
I have to disagree with what was suggested. When making such a big hardware change its usually recommended to reinstall windows. As long as your Win 10 is tied to a MS account it should transfer over without issue.
I'm with Corwin. Best practice on a change such as this is a full wipe and reinstall unless you're well-experienced dealing with the myriad ways treating Windows installs as modular can backfire on you.