Instead of disabling the service group you could just freeze the group. This has the effect of preventing a failover if a resource comes offline outside of the cluster.
When you are finished with your external operations, then you should run the probe command to ensure that the resource is back online and then unfreeze the service group.
The one thing to note in this scenario. If the physical machine was to fail while the SG is frozen, that group will not automatically be brought online on a failover node.
Because it is frozen it will not take any action on the group (online/offline/restart of resources).