As we know all line items are individual here in MIGO.
And also there are no mass maintenance during goods movement in MIGO.
So you may need to go for a development. By using an user exit or badi, you can set the value fixed for all line items or you can set a logic to pick the value automatically as per your selection criteria.
Find an user exit or badi with the help of this document Methods to find Customer/User Exit's & BADi's for a Transaction Code!
Then consult with your ABAP to call the user exit or badi during the transaction MIGO.
