When it comes to large scale events and High Rock Noble Houses I personally operate under some basic rules.
1. Thou shalt not lay a ruling claim to an in-game location.
In other words, no, you can't depose Queen Arzhela and claim to rule Evermore. Not even as a Regent with her permission.
So really, just don't. Those are open and "public" spaces and if one person can claim to be the Earl of Hoarfrost Downs so can someone else and next thing you know we have competing "realities." It's bad form. Really bad form.
2. Thou shalt not play the ruling NPCs.
In other words, no, you can't say Emeric said something disparaging about a player character at dinner or made a ruling against a player character. A caveat, however; All nobles derive their titles, ultimately, from the Crown...and that is High King Emeric. That can ALSO be Queen Arzhela and any other NPC King or Queen in High Rock...but even they ultimately hand out such rewards under the auspices of Emeric. So whether you got a title from a player-character Duchess or said your character got their title from birth, their family having been Lords for generations... in the end there's no way to completely cut out the NPC rulers. A certain amount of "hand waving" is required in this case. And whether "getting your title though RP" or simply creating a character that has a title from jump... keep in mind that both have EQUAL validity, neither is somehow "better" or "more legitimate" than the other.
3. Thou shalt only lay claim to rulership of PLAYER-MADE demesnes.
Wanna be a Duke? Fine. Make up your own Duchy. Bear in mind that the cities on the map are mere snapshots and the "real" map would encompass a much vaster place with plenty of room for other domains of various status. Don't bother to try to lay its borders out on the game map. You'll just generate argument. The Barony of Gawd Du is "south of Northpoint by better than a day's ride." There. Done.
4. Thou shalt not pretend to authority over any player character outside your own demesne.
In other words, those players who have agreed that your character has authority over them. No one else has to listen to what your Duchess says.
Does this series of events conform to all of the above? From what I've been able to glean (and my information retention is not perfect so it's possible I'm wrong) it seems that it does.