WBS change on PO creation wrt Sales Order

Hi Abap'ers,

        While creating the Purchase Order with reference  to existing sales order;  the Purchase order by default selects the WBS element which is assigned against the sales order(while Account Assignment). My requirement is,  i need to check the WBS element while Account assignment on PO creation and update the latest WBS element which i fetch based on some criteria. Is there any Exit/BADI to update the WBS element on screen as well as in table "EKKN".

       Also kindly refer the screenshot for more information.

      Thanking You.

Regards,

Ketan