When we remove additionalTrustBundle CA of mirror registry(user-ca-bundle) that was passed via the install-config.yaml for agent installer installation,
MCO does not remove certificatefrom the nodes.

$ oc version
Client Version: 4.15.23
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: 4.15.23
Kubernetes Version: v1.28.11+add48d0
$ oc get clusterversion
NAME      VERSION   AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.15.23   True        False         3h2m    Cluster version is 4.15.23

    Always

    1.Create cluster with additionalTrustBundle CA in install-config
    2.Locate the mirror reg CA certificate stored on the node's /etc/pki/ directory
     ~~~
     cd /etc/pki/ca-trust/source/anchors
[root@master1 anchors]# ls -la
total 216
drwxr-xr-x. 2 root root     49 Sep 18 05:23 .
drwxr-xr-x. 4 root root     80 Sep 18 05:20 ..
-rw-------. 1 root root 220593 Sep 18 05:23 openshift-config-user-ca-bundle.crt
    ~~~

    3. back up and delete the CM (user-ca-bundle)
     ~~~
   $ oc delete configmap/user-ca-bundle -n openshift-config
configmap "user-ca-bundle" deleted
     ~~~

    4. Observer if some changes happens at the MCO/MCP level due to the same.
    5. Switch to the node and check same /etc/pki/../ to see if CA is present or not 
    

Certificate still present under  "/etc/pki/ca-trust/source/anchors" on the nodes. No new MC got generated

# cd /etc/pki/ca-trust/source/anchors
[root@master1 anchors]# ls -la
total 216
drwxr-xr-x. 2 root root     49 Sep 18 05:23 .
drwxr-xr-x. 4 root root     80 Sep 18 05:20 ..
-rw-------. 1 root root 220593 Sep 18 05:23 openshift-config-user-ca-bundle.crt

[root@master1 anchors]# cat openshift-config-user-ca-bundle.crt | grep "MIID2TCCAsGgAwIBAgIUb1e2U0GXeW5qmTlgzE8SSDvht2YwDQYJKoZIhvcNAQEL"

MIID2TCCAsGgAwIBAgIUb1e2U0GXeW5qmTlgzE8SSDvht2YwDQYJKoZIhvcNAQEL
MIID2TCCAsGgAwIBAgIUb1e2U0GXeW5qmTlgzE8SSDvht2YwDQYJKoZIhvcNAQEL

    New MC should get created once the user-ca-bundle has been removed and roll out of MC should happen on the node. Certificate should be removed on the nodes.