Having auto-sync enabled on the device group is essentially the same as if you were telling it to sync manually after every configuration change. So the question is really whether the change you're making is part of the shared configuration that would be synchronised over to the the other unit.
When you say RADIUS, you could referring to radius authentication to the management interface, or to a virtual server that load balances radius traffic, but in either case, it would be shared configuration, and therefore synchronised
If you disable auto-sync temporarily, and make the change, you'll see the sync status in the top left corner of the GUI change to 'Changes Pending', which means it has changes it needs to synchronise with the other members of the device-group