There is a program called Types:http://types.sourceforge.net/
It's a file association manager, and it's pretty cool. Of all the ones I've come across, this one is my favorite, and it's free. I don't know if it changes icons, but try it...it may.
 it can definitely change the icon, i see it on the screenshots on the website.
Most every other file association tool I've tried is more hairy or quirky than I cared for. At one point recently, I really did an intense search for programs like these, and this is the one I settled for.