This two-piece code will allow you to setup a Nightbot shoutout command which can be customised to allow per-user shoutout messages, with a fallback default message.

Because Nightbot commands have a character limit, you won't get far with including the custom messages directly in your command string.

The solution is to use Nightbots urlfetch variable to fetch a JSON object filled with custom messages from somewhere on the web — here I'm placing it in a Github Gist (which works fine, but a bit slowly). You could put it somewhere on a plain old HTTP page served anywhere on the internet.

How to use

1. Clone this JSON: https://gist.github.com/matthewjohnston4/ef62107655e471384fe027e0738a5c05 and store it where you want.
2. Customise the JSON object to add or remove any "username": "shoutout message" combinations you want (don't forget those trailing commas).