Urgent. User exit to change an ekpo field

hi all, im trying to modify the AUREL in a user or a badi, when i create a purchase order, depending a flield of header... but i can´t... The badi doesn´t works, there arent methods with header and item to change...

I have also a user ( EXIT_SAPMM06E_013 ). It has the tables ekko and ekpo, but when i tryed to change aurel, SAP delete my modification after the user exit.

Help me Please.