Editing the /System/Library/LaunchDaemons/com.apple.pfctl.plist file
Some paths and applications in El Capitan are protected by System Integrity Protection. Even root can't modify the files. You first have to disable SIP before editing or modifying them.


Reboot your Mac to Recovery Mode by restarting your computer and holding down CommandR until the Apple logo appears on your screen.
Click Utilities -> Terminal.
In the Terminal window, enter in csrutil disable and press Enter.
Restart your Mac
Modify the file(s)
Reboot your Mac to Recovery Mode by restarting your computer and holding down CommandR until the Apple logo appears on your screen.
Click Utilities -> Terminal.
In the Terminal window, enter in csrutil enable and press Enter.
Restart your Mac