Once a combo room has been created it's component rooms can only be changed if there is nothing scheduled in either the combo room or it's associated components. Once an event is in any of the rooms the combo room is "locked" and components can no longer be edited.
Locking of the combo room will occur even if all events in the room are in a cancelled status.
To unlock the components you must remove all events from the combo room and it's components.
You may delete a combo room as long as there are no events in the combo room itself (including canceled events). Events in the component rooms only will not prevent you from deleting the combo room.
Please see What Is A Combo Room?, for more information.