Testing some stuff in the scripting terminal.
Is it possible get notified, when the current play position was changed?
Nopes, too much information in too short notice.
The script runs in the GUI thread whereas the sound thread gets the real-time priority.
If you need specific triggers on specific song or pattern positions, you could always monitor a bogus device (midi control device that actually does not control anything) of which you pick a parameter to monitor or listen to and then use effect column effects to change the DSP effect its parameter value (or use the automation for that).
As soon as the parameter of that DSP device changes into a specific value, you can let your script then trigger an action to execute.
Do note that the script does not run and act real-time, so the action may always lag behind.
Ah, ok 
I was experimenting with a midi out device to send note on events to enable leds on a midi fighter. Is there maybe a different way? Timers would be useful, but it seems Tool() is not available in the script editor … With timers i could use the playingobservable to start and stop the timer and in the timer functions i could read out the current songpos.