The following things need to be done in order to change Agent Control Level from Full to None.
Stop the MOM service on the MOM Management Server managing the particular agent whose control level needs to be changed.
Open the Admin Console
Select the All Computer node choose the Management Server and open the properties windows (right click and select properties)
Select the Agent Install Tab and uncheck the “Reject new manual agent installations” checbox
Go to Start/Control Panel/Add-Remove Programs and select the MOM Agent and click Change/Remove. This brings you to the Modify/Remove Mode.
Pick from Manage Agent Management Group options (Used for Add, remove or modify a Management Group for that agent)
In the Agent Configuration dialogue change Agent Control Level to None.
Go to the MOM Admin Console under the Administrator/computer/Agent-managed Computer node select the MOM Agent right click and select “Force to Unmanaged Management Mode” option.
A warning message will be displayed for which select “Yes”
Now go to the Unmanaged Computer node right click on the agent and select “delete” this is required so that all the data associated with the computer is deleted removing all the footprints of the agent.
Select the Management Pack node right click and select “Commit Configuration Change”
Restart the MOM service on the Management Server
Go back to the Admin console and under pending actions view approve the manually installed agents that show up.
Information/workarounds/solutions provided may not be supported by the Microsoft Operations Manager team. Comments expressed by the blogger maybe subjective and are subject to change.