Replacing Non-System Icons

Select your file in Finder, press ⌘ + I or File > Get Info, then drag the icon onto the thumbnail.

This works for most files, folders, and apps.

Replacing System Icons

To replace System icons, you have to turn System Integrity Protection off temporarily.

1. Hold ⌘ + R while restarting your Mac to enter Recovery Mode.
   
2. Open Menubar > Utilities > Terminal and enter the command csrutil disable to turn System Integrity Protection off, then restart.
   
3. Use the Get Info panel or LiteIcon to replace the icons for the apps you want to customize.
4. Hold ⌘ + R while restarting your Mac to enter Recovery Mode again.
   
5. Open Menubar > Utilities > Terminal and enter the command csrutil enable to turn System Integrity Protection back on, then restart normally.
   Your system is now protected, and your icons are customized!