Setting home partition to a separate drive.
 

I would like to install an SSD to replace the existing HDD to get better boot speed. I currently use OpenSuSe 15.1 and will install the same. I would like to install the existing HDD as a second drive and use the existing home partition as the new home partition to save having to copy everything over. Does this make sense? What would I have to do to enable this?

install the new system, create the same user (using the same id/group) and finally mount the old drive (into /home/user). Additionally you may need to copy some files from the initial home dir (before mounting it).

Look at this help page: Partitioning/Home/Moving
Please be aware that advice is Ubuntu based, but may be adaptable to OpenSuSe 15.1.

"and will install the same."

If you will be doing a clean install then used advanced installer to tell it where to "mount" home. I think the original text based installer will do it if the gui installer gives you trouble. Still easy to fix later but why bother.