Programically control mqtt in and mqtt out nodes

In my flow, I set an Interval and I send message from mqtt out node repetitiously.
Now I want to stop sending programmatically without re-deploy Node-RED.
How can I do this?
How can I manage mqtt in/out nodes connections?

a simple-gate node?

Or if you read the help text you will see dynamic connection details.
[edit] if running latest node-red 3+