MacOS – How to permanently disable Notification Center in Mavericks

System Preferences -> Sounds, and set Alert Volume to the minimum. (I'm using Yosemite, and this might not exist in earlier versions.)

To disable Notification Center from the command line, write a KeepAlive key that is false into the /System/Library/LaunchAgents/com.apple.notificationcenterui.plist like so:

sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool false  

If you want to re-enable Notification Center, you’d just run the same with a true:

sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool true  

Method to DISABLE without sudo:

launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist  
killall NotificationCenter

Method to ENABLE without sudo:

launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist  

Then just hit Command+Shift+G and go to /System/Library/CoreServices/ then find “Notification Center” and double-click it to launch it again

Tutorial with useful info here and here