Hey there, Russ_1.
So as I understand it, you are going to do a fresh install of Windows 10 on the SSD and your HDD has Windows 10 as well?
Although some of the games and other programs might work when you install the new OS, some conflicts may arise, because of the two different installations of Windows. The best way to do everything in my opinion is the following:
1. Backup all the personal data from the HDD
2. Connect the SSD and install Windows 10 (with the HDD disconnected during the installation process)
3. After you've installed Windows on the SSD, connect the HDD to the motherboard.
4. Repartition and reformat the whole HDD.
5. Install your games and programs on the HDD and put the backed up data back on it (if you want...