One thing to note is the file system gets changed when you update to 2018.
So I'm not sure you could safely go back to 2016 if you wanted to once you do the update, .. without uninstalling and re-installing everything, which would cause lost data (new realtracks etc at least, hours of songs at worse).

I'd install 2018 over your existing 2016 version, assuming you have BiaB on C: drive.
Then if all went well I'd backup up the 2018 drive onto the old drive and stash it somewhere.

Actually I like having multiple drives of the current version.
I may need to use it in more than one location, so I can leave a drive somewhere else.Like in a drawer at my buddies house.
Planned offsite backup with dual purpose. <grin>

Make your sound your own!
.. I do not work here, but the benefits are still awesome