Hello world.
What you need is two(or more, really) registry files, one for steam setup path( as backup) and second for target game version path. Swap them at will, this makes sseedit see what You point at.
Edit this: [HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Bethesda Softworks\Skyrim Special Edition]
That's it, candy of insight stolen :).