In order to apply custom "visual styles" or themes in Windows 7, you must patch a few system files including Explorer.
I can see from the start how this could be a potential security problem, but how much so? Is there any confidence to be had in the fact that accusations of malicious intent don't seem prevalent?
Lastly, are there any ways to modify these files by hand to facilitate custom visual styles? Input on how safe or unsafe this may be is also welcome.