It would be nice if you could adjust the cost of an item at the time of invoicing. For instance, if you are using an item as you shipping / postage item (in stead of the shipping field). A customer pays a certain amount for the cost of the shipping. During invoicing the actual cost of the shipping charge has changed from the preset cost for the item. You need to be able to change this cost to reflect the true cost and therefor reflect the actual saving/loss on that item.