Hello, Scott.
You absolutely can bring your SU 2018 model into SU 2019 and apply our layers with ConDoc 4.5
No need to start over from scratch if you already have your geometry built; you would just group and apply the appropriate layers to your groups. Check out our Model Organization Guide in the 3D Warehouse.. this will make it crystal clear where to put everything and the guide itself will not affect your drawings.
Give it a go and see how it works for you.