A Group Policy object (GPO) must be controlled by Advanced Group Policy Management (AGPM) before you can edit it. See Creating, Controlling, or Importing a GPO for more information about controlling a GPO.
To make changes to a GPO offline without immediately impacting the deployed copy of the GPO in the production environment, check out a copy of the GPO from the archive. When changes are complete, check the GPO back into the archive and request deployment of the GPO to the production environment.