Scenario:  One S/R Sales order generated by an RMA four four of the same item being sent back for "rework".  We send them out as they are finished, one at a time.  We are charging return shipping.  We will not know how much for several days after shipping because that's how long it takes to get shipping charges from the carrier.  
I see that we can release and print the packing list and invoice and then not mark the invoice as printed and not post the invoice, but how do we add shipping costs which may be different for each invoice?  I am never asked this question during the whole process.