Disabling AirPlay on Mac (Sierra) I used to have AirPlay disabled using the terminal (sudo chmod 000 /System/Library/CoreServices/AirPlayUIAgent.app/Contents/MacOS/AirPlayUIAgent). I just upgraded to Sierra and now it has come back and the old way won't work anymore. 

Any one know why? Or what else I can do?
@scottishwildcat is correct. Most of /System is off-limits to changes so long as System Integrity Protection (SIP) is enabled.

You can temporarily disable SIP by rebooting into Recovery Mode (press and hold Command-R from the time the computer starts until you see the Apple logo), then opening Terminal from the Utilities menu and entering this command:

csrutil disable


Reboot back into Recovery Mode and access the Terminal again. Enter your desired command, then enter this command to re-enable SIP:

csrutil enable


Reboot one more time into macOS as normal and AirPlayUIAgent should have the specified permissions. Note you'll likely need to redo this each time you upgrade macOS.