Hello,
Not sure if this will help you, but you can update the vendor information in VENMAP using transaction
BBP_UPDATE_MAPPING.
Check note 357201 about it and also the following link, which contains additional information:
Mapping Backend Vendors to Business Partners
http://help.sap.com/saphelp_srm40/helpdata/en/95/f6a93e08503614e10000000a114084/frameset.htm
Regards,
Ricardo