Yes, this is correct.
See this, near the bottom: Rule Machine API
It says Global Variable, but it actually sets Hub Variables for a 5.1 rule.
You still need to have the rule as it supplies the endpoint. And, it will be triggered by setting the variable. I just found a bug too: if you remove an endpoint trigger, it still works and still triggers the rule. I think this is easy to fix, and the fix is such that the variable would be set but the rule wouldn't be triggered without the endpoint trigger.
