Temporarily disable Notification Center in Mountain Lion from command line?
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