Yes, you can do this.
In Wordpress, simply change the featured image. Then add a space and then delete it from the post. Then press update, and preview or view the post.
We use the update time of the post to know when to update the meta-data about a post.
Unfortunately, WordPress does not consider changing the featured image to be an update, so the add space workaround is necessary.
If you are planning to make many changes or add images to many old posts, drop us a note at email@example.com. We can schedule the system to pick up the new images.
The method is the same for other publishing systems as well. Make the image change; trigger a post update. If you are making big changes, drop us a not at firstname.lastname@example.org and we'll schedule a bulk update.