Not sure about your question… you want to set your own No. on Sales Header when you create a new Order (for example) OR you want to change the No. of your actual orders?
Handling depends on the way you want to handle that:
add your field shipset to both tables (T36, 37)
a) if you enter the shipset BEFORE adding the lines, go to the sales line table and look at the code of OnValidate Trigger of field No. There you can identify a paragraph where information is populated from the header.
b) if you enter the shipset AFTER adding the lines go to the sales header table and look for the code in the OnValidate trigger of e.g. field Shipment Date. A function ‘UpdateSalesLines’ is called. You can do something similar…
c) BEFORE or AFTER creating sales lines: combine both
I think Joerg is on the good way to inform lines with the Shipset value of the header but if you don’t want to make another calculations with this field on lines… couldn’t you use a FlowField?, this would just display on lines the header value for Shipset [*-)]
Agreed, the flowfield is a possibility if you are sure that you will not have several different shipsets in your sales lines, only using the header information as default…