Enhancement for VA02 on Ship-to-Party field BSTKD_E(Purchase order)

Hi Guys,

   I have a requirement for VA02(Sales Order change) ship-to-party field BSTKD_E(Purchase order no).

Initial Requirement:

When we provide any sales document number(1111), it should automatically hide the ship-to party field(Purc order no) value(i.e.,click on  item no->order data->ship to address),and moreover it(Purc order no) should display when we click on 'SAVE' .

Can you guys suggest me any enhancement(Badi/Exit).

For clear idea i am providing the screenshots.

Regards,

Sujay.V