read the current wishlist (if you did not notice it, it is right at the top of the screen with letters in all caps saying READ ME FIRST. However, since you did not notice that, I will post a link for you here.
Why not enable the file extensions in the Windows Explorer options instead? It's a much easier and more "clean" solution. I don't think icons should change, icons tell you the program that is used to open the file, not the kind of the file itself. Plus the extension "carries" more information about the file and is also easier to understand than an icon which can be misleading or similar to another.