Is there a way to override only a portion of the function print_media_templates defined in wp-includes\media-template.php?

No, there isn’t. Unless there’s an apply_filters() call, you can’t modify any of the output. You mentioned “the only hook is to the entire function”, but that’s not the case either. There is a do_action() call at the end, but this is an action hook, so it only lets you run something at the end … Read more

WordPress Media Uploader not displaying image that has just been uploaded

Your issue sounds like a visual bug in the WordPress Media Uploader’s interface after an image has been uploaded, especially since you mentioned that the image appears in the right-hand preview pane but not as a selectable thumbnail. Try to force refresh the media frame after upload. You can use the add:attachment event to force … Read more