Forum Discussion
I don't think there is an option a device to be primary for GTM sync as on which you make changes will update the others.
You can also check this article:
https://support.f5.com/csp/article/K14044
First I think better stop the synhronization as if you are doing an upgrade of an F5 GTM device, then change the sync group name and then do the rest as if the sync group names don't match the gtm_add will not work also because you have already done gtm_add maybe after you disable the synchronization and change the sync group name and again enable the synchronization there will be no need to run gtm_add as the device ssl certificates are already exchanged.
https://support.f5.com/csp/article/K11661449#disable-sync
Can someone extra confirm this as I haven't done DNS splitting myself?