Well I have certainly edited one before. What you do is you export the chipset using the export thing at the top. I use paint, I don't know why it worked for you. Open it up in an image editor and mess with it all you like. Each tile is 16 by 16 pixels. When you're done, save the changes, rename the chipset, and import it. After you click import, don't forget to make the flashing part be the not included part (usually pink). Hope this helps.