You can follow these steps to change/update the credentials used for a single agent or group of agents in a MOM 2005 Management Group.

1.  Change the password for the account used as the Agent Action account in Active Directory.

2.  To find the agents that are using a particular Action Account, run the following query against your OnePoint database:

use OnePoint
Select Name, Value
from Attribute INNER JOIN Computer ON DISCOVERYCOMPUTERID = IDCOMPUTER
WHERE ClassAttributeID IN (Select ClassAttributeID from ClassAttribute where
ClassAttributeName = 'Action Account Identity')
AND IDComputer IN (Select DiscoveryComputerID from Attribute WHERE
ClassAttributeID IN (Select ClassAttributeID from ClassAttribute where
ClassAttributeName = 'Action Account Identity'))
order by value, name

3.  In the MOM 2005 Administrator console, navigate to Administration > Computers > Agent-Managed Computers.

4.  Select all the agent-managed computers that are using the Action Account for which you are changing the password.  Refer to the results of the query in step 3.

5.  Right-click on the selection(s), and choose All Tasks > Update Agent Settings.

6.  Enter the new Action Account credentials.