Is it possible to add an composer button to att this
I haven't installed it yet. Can I use this for sending data to non-slack webhooks? I'm looking to send topic notifications to NodeRed (an automation platform) for further processing.
I don't believe so... the slack plugin (which I only have a brief recollection of) connects to slack directly, and can't be customised in the admin panel.
You'd probably want to create your own plugin with integration into NodeRed (or reach out to us for a quote for a similar plugin)