Hello Ram,
Kindly check as below
S002 is standard Sales information structure.I think it wouldn't be recommended to add field VKBUR to S002.
S6 series is provided by SAP for custom LIS development. I think you should add your field VKBUR in S600 which invloves considerable amount of work.
However, also kindly note that the maximum characteristics available in a LIS is limited to 9.
Kindly share If I have understood your query and answered suitably.
Regards,
Pon