I don't want to fill the conditions, but I tested if I fill it could change the value but not worked
I made the worst work-around to fill the net price right:
After BAPI_PO_CREATE1 and BAPI_TRANSACTION_COMMIT , I did it:
DATA: w_ekpo TYPE ekpo.
SELECT SINGLE * FROM ekpo
INTO w_ekpo
WHERE ebeln = v_po_number.
IF sy-subrc = 0.
w_ekpo-netpr = v_net_price.
MODIFY ekpo FROM w_ekpo.
ENDIF.
I agree, it's horrible, but... worked