How to update Landed Costs on Inbound Shipments?

Is it possible to update the landed costs (Specifically Duty and Ocean Freight) once the inbound shipment has been received and billed? For 95% of our shipments, we have variances in the freight bills and they need updated after we receive the bill which could be 2-4 weeks after the product is received. We previously were not using the inbound shipment and were just receiving the PO with multiple items and then had 1 item receipt so we would then adjust the item receipt. The problem with the inbound shipment is that it is creating multiple item receipts for the