Is there any way for AppleScript to get notification or something similar when xyz preference changes in plist-file?
Monitoring when file modification date is changed is not good idea, because this plist-file has lots of preferences and it changes alot.
plain AppleScript cannot register to notifications except the provided event handlers like folder actions or Mail / iCal events.
You could do this in AppleScriptObjC
I’m total newbie in ASOC. How hard this is to do?
Harder than AppleScript Studio. You have to learn the basics of Objective-C