HOWTO: Manually Change Icons in OS X

Note: I am not responsible for any damage you may cause to your computer. If you don’t feel comfortable mucking about in applications resources I implore you to just shell out the $30 for CandyBar

1. Find an icon you want to use. They need to be in the .ICNS format. DeviantArt and MacTheme Forums are great sources.
2. Go to your Application folder.
3. Right click on the App you want to change.
4. Select “Show Package Contents”.
5. The icon is located in “/Contents/Resources”, and generally there will be named “app”, “appicon”, or the name of the application itself. Just look for the .icns extension and a high res graphic.
6. Rename your downloaded icon to what the icon you found in “/Contents/Resources” and copy it over.

That should work, but you may need to log out and log back in.