Account Generator Customizations and Extending Entity Objects

 The 11.5.10 iProc Implementation Guide states on page 2-34 that you can add attributes that cause charge account re-defaulting.  It further states you can extend the Entity Object for requisition lines or distribution lines.  I have successfully extended for attributes for a requistion line.  However, now I need to add an attribute at the header.  Since the implementation manual only states you can extend lines and distribution lines, is extending (for the purpose of charge account re-defaulting) only limited to lines and/or distribution lines?