As this is a place to share what has worked, leaving this here as I spent way too much time figuring this out, when it was so silly simple.
When you have your own script, or a third party one attached to a gameObject as a component, and you want to execute a function from within that script - this is for you. For example, I have a dissolve shader with a small script that handles dissolving an object (and brings it back) - pretty handy for death or teleportation. So to call that function via schematic, it’s literally as simple as a single node in Makinom, and then called via any Machine your using to launch a Makinom schematic.
Here is a screenshot with the fields filled in per my example, hope this helps someone!