Edit an Item Fulfillment record that has already been shipped

We have a script that creates an inventory adjustment fort the consummables used in an item fulfillment (box, packing material, etc.) that once the item is selected from the UPS/FEDX it correlates to a custom record in NS that has a "bom" for that item that ties to the NS item number.  At the end of day all fulfillments that have been processed, the scripts adds up the boxes, etc. and creates an Inventory adj for the day for all the consummables, taking them out of stock to shipping expense.  The issue we are having is when an item fulfillment