Hi,
Its not possible to create a pre-declaration directly from the BOL unless there is a reference to the IBD. You also cannot assign a sales order to the BOL.
You can create a customs bills of lading automatically from a feeder system, you can use interface /SAPSLL/API_6800_CFB_SYNCH. To make changes to existing customs bills of lading, use interface /SAPSLL/API_6800_CFB_CHG. But I have never seen a sales order used as the referencing logistics documents.
Kind Regards
Ann-Marie