http://elderscrolls.wikia.com/wiki/The_Whispering_Door#Trivia

If all the dialogue and script are there, is any one interested in modding the murder of Balgruuf and the crowning of Hrongar? I'd love to see his own kids murder him...

Not enough dialogue left to put it back together, but you could perhaps cobble together Elisif's murder during "Boethia's Calling."

As an aside, I'm working on something that, as a consequence of what it does, will allow you to kill Balgruuf yourself, and Hrongar will become the Jarl of Whiterun and take Balgruuf's place during the siege and every other quest Balgruuf's involved in.

Well, now I'm very curious. I hope whatever it is becomes public.

It's nothing terribly special. I'm waiting on the USKP 1.2.1 release, mainly, but it's almost complete.

I got so tired of the inexpert "no essentials" mods that I decided to make one myself, that attempts to remove an actor's essential status when quests involving them are complete. Important NPCs, or those useful to the player in some way, are protected rather than being essential, and killing an NPC will fail what quests they're involved in.

So once "Dragon Rising" is complete, the player can kill Balgruuf and Hrongar will become acting Jarl in his stead. Hrongar has appropriate dialogue to fill Balgruuf's shoes for the main quest and the civil war quests, and Ulfric and Tullius speak of Hrongar rather than Balgruuf.

Unfortunately, Hrongar's rather weak stat-wise, so the siege of Whiterun is a cakewalk once you get to the throne room. Oh well.

The only trouble is that it makes odd decisions like helping Ulfric take Skyrim and then killing him viable. I also didn't edit any dialogue, so NPCs will still talk about other formerly-essential NPCs being alive.

Protected, so they receive less damage at lower hp? Any mod that's going to put Balgruuf in the ground and Hrongar on the throne is awesome.

And you mentioned Elisif could be killed, does this mean some one replaces her?

More than likely he means protected as in you "kill them" and they lie on the floor like your follower does, then you hit them again and they die. Protected from killing them, but not stopped if you want to.