This is likely what I will do now that I have given it some thought. This will bring over all of my installed apt and snap packages, right? And they will both be aware and know how to update from there?
I have the NVMe prepped. It has a fresh Ubuntu install of the same version, but on btrfs. I could probably even snapshot it before I get started to make sure I can roll back and try again if I fuck up. And worst case, I can just reinstall the OS on that partition, as it would touch my existing install. It feels pretty safe to try. Worst thing that can go wrong is I waste my time.