I have successfully moved back and forth between the 2 platforms multiple times. No issues noted with either platform up to this point.
Caveats:
Obviously only 1 application can work at a time.
Specific Z-Wave devices supported by one platform may not be supported by the other.
HomeSeer keys are in the Z-Wave INI file, but the format is slightly different, there is a post on their forum on how to format correctly.
I have no experience migrating the S2 key.
I’m using a Z-Net device so the Home Assistant connection is IP/TCP Port, not serial.
My process:
Disable the HomeSeer Z-Wave plugin under the Manage Plugins page.
Point the Z-Wave-JS UI configuration to TCP://IPofZNET:Port
Enable the Z-Wave-JS Integration
Start Z-Wave-JS UI Add-on
Watch the logs. If it’s been a while, it will take 30-60 minutes for the startup interrogation to completely sync.
If I added new Z-Wave devices to HomeSeer, they are added to Home Assistant.
Note: I’ve only added/deleted devices via HomeSeer. Not sure if you could do this in both, but my gut says it would probably work fine as Home Assistant adds any new devices I added via HomeSeer without issue (other than potentially not recognizing the device).
My suggestions:
Backup both platforms before starting.
Make sure you disable the Add-on and Integration in Home Assistant while actively using HomeSeer.
Check logs carefully when switching.
So far neither platform has done anything to the controller that made the other fail or even unhappy in any way.
Good luck.