Suggestions:
In Supplier Master, Users can enter/ update the code of the transporter through which the material is to be delivered any time, even after the supplier is used in further transactions. You can select the relevant transporter code from the pophelp . It must be defined in the supplier or transporter master if entered. Transporter code defined in supplier master gets populated in further transaction for that particular supplier. Note: That supplier code does not get non editable after using the supplier code in transactions.