Yes you can. When you unpublish, the hub remains unseen until you are ready to republish. Deleted hubs, however only stay for 24 hours and then they are erased.
The reason your hub is not read is because it is pending. It is not available for all to see just yet and may not show up in the feed. Your hubs stays pending for at least 24 hours before the search engines get to crawl it.
You can edit your hub without unpublishing it by clicking the edit button which is beside the delete button. Add your photo and save.