Maybe its time for me to write up another guide with all those neat little bits that I have come across in my 4ish years of playing this game and tinkering with its interface.
I can tell you a risky but quick way to do it. Replace the icon files in the directory world of warcraft/blizzard interface art/icons with ones you like. just rename your icon file to be the same as the ones in the directory already. make sure your new icon is the same file type and dimensions. theoretically it will work.