User exit/BADI for condition type in shipment costing

Hi! Does anyone know of any user exit or BADI or function module we can use to populate a value to a custom condition type we have created for shipment costing? We want to calculate the customs duty charges based on the purchase price of the item in the PO. As such, we need to go extract this information on the PO and populate it on the condition type.

Appreciate any help on this.

Cheers!

SF