ShipStation provides an option to create another shipment within orders that have already been shipped.
Once you create the first shipment for an order, ShipStation replaces the Configure Shipment Widget with Additional Actions:
Simply click Create Another Shipment and you can create a new shipment within the order record.
NOTE: Since these are new shipments, ShipStation will try to send new customer notifications and marketplace notifications unless these options are first disabled on the order.
For a smoother notification process, check out these features:
These features are the most efficient methods to use to ensure your customers and marketplace are updated properly with the correct product information.