I've changed the codes of presets before to make them transparent or to have different patterns on each side/two different eyes, but never anything like this. I've never made markings, though.
When I tried making the markings for the preset I'm attempting to make, I made a separate layer from the base I made earlier. After I finished the marks, I switched to the base layer and erased, but instead of it turning to the grey checkered thing (meaning a transparent background) it turned black where I erased it.