RE: Manufacturing BOM Cost
Hi Dom,
Note that this was verified in GP 2018, however, may work the same in GP 2015.
You could do a manual override to update the BOM cost on the BOM Entry window. If you click on the calculator icon next to the BOM Cost amount, it will open the standard cost maintenance window. From here you could select Override checkbox on whatever fields you wish to change. Then you would use the Go To icon to enter the Roll UP and Revalue window. After this is done, clear and reenter the item in BOM Entry window and you will see that the BOM cost field is updated.
DISCLAIMER: Highly recommend you consult with your finance/accounting team before doing this, however, as it will change the inventory value for this item.