I'm attempting to make an easy wordpress plugin that sets experience image. I've it from the media library to ensure that whenever you click "Place into Publish" it will a custom function. However, clearly this practice function is undesirable in almost any other context. As a result I must create a separate button "Make Background" that will call the custom function. Any ideas?

Thanks

You could utilize featured image as well as custom area template having a upload area, then when you load the page you need to do all of the CSS stuff.