No plans to make an app at the moment, it must be done manually
at your own risk.
Tested in 10.12.4 to still work, but new instructions must be followed:
In Terminal, unload Notification Center:
launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist
killall NotificationCenter
Replace /System/Library/Frameworks/NotificationCenter.framework and /System/Library/CoreServices/NotificationCenter.app with the ones in the patch, then restart macOS.
Reload Notification Center:
launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist
Restart macOS once more.
This is untested in anything above 10.12.4, so backup the original files just in case. It's also probably not update-proof, and you may need to replace the components every so often.
http://fox.furcode.co/macOS/DarkNotificationCenter-foxlet.zip