Displaying text in material sales text in VL01n

Hi Experts,

I have requirement like below in VL01n.

Before saving a delivery in VL01n, I need to read BOL flag(it will be stored in MARA table by adding one custom field in MARA table) for each line item in the delivery and if BOL flag is available, Import BOL flag from MARA table for the line item and put word “HAZMAT” in delivery item material sales text field after clearing any previous text (if it is there) .

Delivery item-> Text-> Material sales text (here I need to put word 'HAZMAT').

Could you please tell me, how I can approach to reach this requirement?

Kumar.