unload nfsd - Operation not permitted while System Integrity Protection is engaged
Firstly, you'll need to disable the "System Integration Protection":

How to Disable System Integrity Protection

And now, you'll be able to disable your "Notification Center":

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


And then, kill the current instance of "Notification Center":

killall NotificationCenter


When you reboot, isn't necessary to do that anymore...

I hope I've helped

PS: Don't forget, at this point your root user will have all permissions. I recommend to reboot into recovery mode one more time to enable your System Integration Protection:

csrutil enable