I searched around a bit...
There is a way to change it, however i warn you before hand:
-It can take a long time to do.
-You can srew up your original icon cache. BACK UP PLEASE!!!!
- only works on 32bit OS for the moment.
The program its called Reshack. http://www.angusj.com/resourcehacker/
This is where it gets tricky, you need to search for the right resource. Start of with shell32.dll. Open it with reshack and in the left you will see a bunch of folders. Open the "Icon" tree, you will see lots of numbers. Now starting at the top, open the first number, there should be a file called "1033". I f you click an that an icon should appear on the main screen. Now navigate to the ones you need changing. When found, right click on the 1033 file in the tree menu and click on replace resource, select your new icon and the icon will be replaced.
Hope this helps... I used reshack to modify my system properties screen and control panel icons.