You could install 3 skins and put the different icons in each skin. Then assign a skin to each catagory with the buttons you want in it.
I do this on one of my sites.
www.greatlakesfisherman.com If you click on the hunting catagory, or the walleye catagory, you will see the different skins. The only thing that does not display correctly, is the forum home page. It only displays one skin.