P49005 and plugging in custom BSFNS

Hi folks,

I've been tasked with generating custom shipment references and I've stumbled across P49005.

Here you setup rules of your own to help create the REFN. Hard coded, NN, UDC or BSFN call.

Has anyone tinkered with the BSFN call? How is this integrated and fed back to the P49005?

Thanks

John