how to configure WordPress to replace uploaded posts (not post a new one)

I am working on automating updates to my affiliate marketing site, using Postie to create new posts and to update (replace) existing ones. I have Postie working, but old copies of posts (same category / same name) are still around after the newly posted replacement is published. How do I configure WordPress to remove the old copies instead? Or, is there a plugin compatible with 4.6.1 that will do this? The old duplicate posts not only show up in the “All Posts” page, but they show up in the site’s index, too. Not good.

All of this, when I’m finished with it, will happen via cron on my Mac, whether I’m anywhere near the computer or not, starting from grabbing merchant datafeeds via ftp to posting updates via email (Postie) with one big /bin/sh script running the entire process, probably around 0200 every few nights.

Thanks!