After you edit the PO, an email notification will be automatically sent to the supplier. The new version of the PO is sent to the supplier to reflect the changes made.
Users will be required to leave a note when they go to save the changes and there will be an instance date and time stamped on the Activity Log of the PO. However, the activity log is not shared with the supplier. The note that you leave when editing a PO is only for internal purposes.