Hello! And thanks for being part of our community!
At this time, there are only a few actions that can trigger automated behaviors in ShipStation:
Updating any type of order details in ShipStation or adding/removing a tag cannot trigger any type of notification for your customers. There may be a 3rd party solution provider that has an existing solution or could write a custom script using ShipStation's openAPI that could detect certain tags on an order and then perform an action, like sending a notification to the customer, but that would have to be managed and triggered by that tool. It's not something that is currently built into ShipStation.