Unfortunately once the initial wallpaper is set, we can’t alter the image file anymore. Even not by setting different initial wallpapers for each script tab. Because the last applied wallpaper will be the one and only initial wallpaper for the whole instrument.
But we can either offset the initial wallpaper that means moving it via set_skin_offset or we can use a label element to set up multiple backgrounds which is covered in this article. Even dynamically like switching them when hitting a navigation button.