Modify the order/invoice with Crystal.

Why don't you change the Crystal report that prints these documents?

Not a problem. I have been doing this for several of our customers and it works great. The setup is fairly easy. Lets say you have a customer by the name of Acme Products and their customer number is ACM452. Create a new price list called ACM452 (this makes things much easier to track later down the road).Open up item pricing and bring up a part that has needs to have their customer number. Just click new and for the price list code use ACM452 and type in their part number at the VERY BEGINNING of the description and type in their price. Click save. Now go to customer and change their price list to ACM452. Do this again if they have multiple ship to locations. Now when you type in a new order for ACM452 their price list code will be ACM452 and when you type in that part number it will pop up with their price and their part number. On the crystal report for both the packing lists and invoice I would change the line that says description to Customer part Number / Description and that way they will see it on the packing lists and invoices.