There is easier way of pointing agent to new oms in 11g.
Go the $AGENT_HOME/bin and execute just one command,
$ ./emctl switchOMS https://oms_hostname:1159/em/upload
Oracle Enterprise Manager 11g Release 1 Grid Control 11.1.0.1.0
Copyright (c) 1996, 2010 Oracle Corporation. All rights reserved.
SwitchOMS succeeded.
If you have agent registration passwd enabled, do the below steps,
$./emctl stop agent
$./emctl secure agent ‘pwd’
$./emctl start agent
Before 11g, you will have to follow steps given metalink#413228.1
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