The first event starts everything off is this one:
Event id = hre_event.1 "The Shadow Kingdom"
It pulls whoever gets it out of the empire - No Choice.
It the triggers other events giving the other Italian princes the choice to pull out or not.
(The AI will always accept unless it is a vassal of the Emperor in which case it will always refuse.)
There are other parts dealing with HRE Italian territory held by non-princes, and notifications.
The basic options for avoiding event #1 are:
Expand the HRE to all KoI provinces. I am having trouble thinking of any way to do this without conquering (and core-ing) all of mainland Venice and the Papal States.
Make sure it has no valid targets. Any HRE prince with a capital in Italy who is not the vassal of a German overlord can get this event
Hab mal gesucht weils mich interessiert. Wenn ich das richtig verstehe ergibt sich das Problem nicht als Italien, da man alle relevanten provinzen ja schon besitzt oder erobern kann. Ausserdem bekommt man ja die Wahl im HRE zu bleiben oder nicht, und kann dann einfach im HRE verbleiben.
Oder?