1. Place a group in the editor.
2. Double-click the group object, set a custom callsign, e.g. "My Group 1".
3. Test the mission, type in side-chat and note the custom callsign being used.
4. In the editor again, cut & copy the group (CTRL+x & CTRL-v).
5. Open the group object and check the variable & callsign. The callsign will have rest to a default value.