Is it possible to disable the thiny "target of the target" green health bar displayed above the mobs enemy when they are in aggro with the tank?

Yes, this is the Tug-o-Threat meter. You can disable it under the Threat section

This issue is stale because it has been open for 90 days with no activity. If you feel the issue is still relevant, please leave a comment to prevent the issue from being closed in 30 days