How to update the output_type of item in process workdef from product to BY_PRODUCT through FBDI

Hi, we use process work definitions where there are two outputs mentioned as output type as product. But we wanted to change the other item as BY_PRODUCT, when we are doing it manually it works, but when doing through FBDI, the file loads successfully but the OUTPUT_TYPE is not changing to BY_PRODUCT from PRODUCT. Can anyone has any idea on this?? or how to do this??