PO Revision Email Workflow

We are activating automatic notification of Purchase Orders at the Vendor level in Oracle.  As a purchase order is created and approved, Oracle automatically e-mails (and/or eventually faxes) the order to the vendor.  The problem is that every time the order is revised, Oracle tries to automatically send the notification again and has to be manually stopped.  I would like to have the process reversed for revisions of purchase orders.  Revised purchase orders should not send an automatic notification but should be able to send notification manually if needed. Is this possible?  Or is a workflow customization required?