1. Find the file/icon that contains the icon you want to use. Select it, and then click File > Get Info.
2. Click the small icon in the upper-left corner of the info window... it will appear to have a small colored halo (probably blue, but it could vary depending on your appearance settings) around it. Click Edit > Copy. Close the info window.
3. Click the icon for your hard drive, and then click File > Get Info.
4. Click the small icon in the upper-left corner of the info window, and then click Edit > Paste.
I thought this was a silly little program, but it has been worth it. It makes the changes quickly and easly. For thoes bezels that requrie going into terminal to change, it makes it a whole lot easyer (and safer). It isn't needed for the odd icon change from time to time, but if you like to customize your icons from time to time in groops, then it is worth it.
I suppose that somebody has created an Action for changeing icon sets, and if somebody hasn't perhaps this is your chance.