Here's the deal: when I login into my KDE environment, I want system to check if my large monitor is connected and to switch to this monitor if it's found. The laptop screen I want to turn OFF (the system heats up enough with only one screen used; besides, I couldn't find any real use for 2nd monitor, probably because of lack of imagination).
After playing a bit with systemd, I gave up and simply added a script to KDE's autostart.
Here's some information one need to get before you write such a script for your configuration: