There are two simple ways of changing the an application's icon on a Mac.

1. Navigate to the application in Finder
   
   
2. Enter the package contents of the application
   
   
3. From here there are a couple of ways to set the icon but the two major points are:
   
   
   
   • The icons are located in the Resources folder of the Contents
     
     
   • The icons are referenced in the Info.plist located in the Contents
     
     
4. So the two simplest methods are:
   
   
   • Replace the current .icns file with a new one of the same name and not make any changes to the Info.plist
     
     
   • Add a new .icns file and change the Info.plist so that it references the new file name instead.

This can also be done with 4D code, simeply by accessing the locations and performing one of the two actions above.