Validation to prevent Assign Driver to More than One Shipment

Need to make Action Check to prevent Assign Driver to more than one shipment except for a certain condition.

I managed to write the Condition in SQL and Tested it externally and works fine but in OTM When I choose the Audit Action "Assign Driver to Shipment" and Post Action Check, OTM fire error (Post action check is not supported on action ASSIGN DRIVER TO SHIPMENT)

Unfortunately, in my case the Validation won't run except for post action check.

Is there are any other audit action that support post action and have same effect of assign driver to shipment ?

Can I Somehow modify the action to support post Action ?