dynamic loadbalancing using value from node

but can i Trigger the script via external montior?

Absolutely, and there a few ways to do this. The easiest is simply to place that script in /config/monitors, then create an external monitor script in the GUI that points to this script and assigns a bogus pool. You need the pool assignment to make the monitor work, though it doesn't have to be tied to anything that you actually care about. Doing it this way also ensures that everything is backed up in an archive.