There are three different ways to do this.
- On the PO for the vendor, you will have to click the Options and then Text, and enter into the textbox.
- To enter temporary messages to all vendors: Go to System Administration -> Control File Maintenance Menu -> System Parameters Menu -> Define Site Control Parameters (LG0144) -> More Purchasing (LG1542)
- If you want to change instructions on the PO permanately, then you have to update the KeyDocs template.