Warning: This procedure will lead to Node drains, node restarts and - as a result pod restarts! Prepare accordingly!

To change the pull secret of an Openshift cluster (e.g. because you switched Red Hat accounts), save your new pull secret you downloaded from cloud.openshift.com in a file, lets call it my-pull.secret. Then execute this oc command:

oc set data secret/pull-secret -n openshift-config \
  --from-file=.dockerconfigjson=my-pull.secret

Of course you’ll need the proper permissions, I assume it’s Cluster Admin, but I didn’t test the exact permission requirements.