I see some problems.
Games and apps currently installed will need to be reinstalled if they use the registry.
A clean install will give you a new and empty registry.
You can export your other files and settings to your hdd using windows easy transfer.
After the new clean install which will wipe out your current ssd, you can import them back.
Again, your apps will need to be reinstalled.
The HDD needs to be disconnected during the clean install. If connected, windows will put some hidden recovery partitions and you will forever need the HDD to be able to boot.
Likely, your new motherboard and cpu will boot with your old windows. Assuming it does, all you need to do is to install the new drivers that come with your new motherboard.
If you want, you could back up your current windows drive to the hdd using windows backup or any other backup app.
In the event of a failure, you should be able to restore from the backup.
I never like to count on a backup that I have never tested.
I have standardized on Samsung ssd devices. I use their ssd migration utility to copy my C drive to a new ssd.
Perhaps it is a new pcie m.2 drive or a larger ssd.
In the event of a disaster, I still have the original ssd which I know still works.