New group & All managed devices

Hello BackDoor, sure there is... here's some steps for you.
 

1. Create a group call "placeholder". All groups that you permanently want to keep will go in here (later we'll move them out).
2. Create a SmartGroup that contains devices, and have it contain "all devices".
3. Next, remove any existing rules and a new rule add one that removes devices within the "placeholder" group you just made.
4. Fire up a new session and navigate to placeholder (perhaps in the full screen / noc mode), and refresh as needed while you assign devices to your new groups.
5. When you're finished creating groups and assigning devices / monitors, select everything in "placeholder" and move that to "My Network"