No, there is no way to access images on disk when loading an HTML file using the pak:// scheme. This would OBVIOUSLY be a huge security risk from a browser perspective, so it’s not going to happen. If you don’t want to package your game every time in order to swap out the images, why not setup a blueprint like this:
These are things you really need to start figuring out on your own or you’re never going to get anywhere. I don’t mean that to discourage you from making games, everyone has to start somewhere, but you need to learn to become RESOURCEFUL. I wouldn’t expect you to know about the URL schemes or image loading and the browser security and all that…but it never occurred to you to load the widget in two different ways based on development vs production…