Since the MNICB is most likely in use, I would use the offline method of configuration. That would not involve shutting down the apps, simply stopping vcs everywhere (hastop -all -force), make the changes and bring it back up starting with the system where you made the changes.
However you make the changes, be certain the active port used by MNICB is not the one you plan to remove and replace otherwise you could unintentionally cause a fault.
You will also need to make sure you have an IP address on the new port prior to configuring it in the MNICB resource.
I would do the following:
make sure the mnicb port in use is the one I plan to keep in the cluster, if not move it
haconf -makerw
hagrp -freeze -persistent
haconf -dump -makero
hastop -all -force
{{{{ here you edit the main.cf and check it with hacf -verify, bring up the admin IP on
the new port }}}}
hastart
{{{ verify the new config is up}}}}
rlogin to other systems and do hastart
{{{{watch the MNICB resource to be sure it is ok
{{{ if you got it right, then:
haconf -makerw
hagrp -unfreeze -persistent
haconf -makerw
