LiteIcon

About System Integrity Protection

The new SIP (System Integrity Protection) feature introduced in macOS El Capitan prevents LiteIcon from changing many icons, including:

All system icons.
Most Apple apps icons.

Modifying these icons requires disabling SIP. Since this process is a little bit tedious and tweaking macOS internals is not recommended by Apple, it's up to you to decide if it's worth it.

Follow these steps to disable SIP:

Restart your Mac, holding down the Command-R keys until the Apple logo appears, to boot into Recovery mode.
From the Utilities menu, select Terminal.
At the prompt type the following command and press enter:
```
csrutil disable
```
Restart your Mac and LiteIcon should allow you to change all icons.

After changing the icons, you should re-enable SIP by following the above steps, but using csrutil enable instead.