Change system files

I'm a complete noob at modding my mac pro and for some reason I keep getting an error that I don’t have permission to rename the item “SArtFile.bin”. I also can't tweak any of the other system files. I am the admin too. I have clicked pressed Command + i. Clicked the padlock on the bottom and entered my admin password to unlock and I still get the same error that I don't have permission to change the files. Thanks for any help. I am running the latest version of SL.

 

I am looking change the system files to customize the look of my icons and UI that I can't achieve using candybar. I guess I shouldn't have said noob. I am just unaware of how to get around this permissions issue.