Hi Jacob,
Thank you for your response.
Initially I have suggested the same solution but users are not ready to accept. The issues is, we have 100 to 1000 lines in purchase order and based on customer requirement the routes need to changed.
If I use the shipping condition user need to change the lines manually one by one (Because the fast change is not possible for shipping tab fields) but if I use the shipping instruction then it is easy to change through fast change mode.
As per the SAP note 356628 it is difficult to add the new fields(shipping tab fields) in fast change.