or better, you can use SICC (SICC - Sense Icon Cache Clearer) http://forum.xda-developers.com/showthread.php?t=662233.
I've found a bug/feature in manila which prevents some icons to be changed.
Since many users were complaining about not being able to change some icons I've started investigating the problem and found that if you try to use a custom icon which have the same filename of one of the images found in \Windows then Manila will always load that instead of your customized one.
In order to easily fix the problem, just rename your icon
This bug affects ONLY manila, therefore in the start menu everything will look fine BUT in the Homescreen you will always have the original icon!]