Yes you can change the system apps icons, but its not as easy as overwriting the dll's.
Example: the location of the original icon could be....
"\Windows\shell.dll -1004"
and the location of the desired icon WON'T be in that exact spot:
"\Windows\shell.dll -8000"
UNLESS...... someone puts the icons in the EXACT spot.
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I'm seriously thinking about making a .dll to change the icons, and hacking into the registry, and change where the apps look for the icons, to that dll.
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Nothing I do seems to get me any closer.....