I think Verse of Darkness meant this , which was an idea of Amerision. I remember reading it before I joined up (I think, my memory is hazy). Either way, they both have the same Butterfly effect. One tiny thing happens and it snowballs out of control.

About the idea of Harry manipulating Luna, I think that's shaky. Most likely, if you go with house-change idea, he ends up in Ravenclaw for some reason (a new determination to learn so none of his freinds get killed) he ends up with Luna being an annoying person to talk because everyone else shuns him. Eventually she becomes his friend, and will most likely do anything for him.

And by having Luna as his friend, you have the chance to introduce the 'Deathly Hallows' several books early. Hearing about the Ressurection stone, he seeks to find it so he can revive Ron (or Hermione, if she dies too) and that would be an entire plot throughout the next 5 books if you rewrite them all from then on. Eventually that would become boring, so you entwine the plot of the books with the overall plot of the AU.

Sirius would be able to escape Azkaban though- a student's death is unlikely to go unnoticed for long, and there would also be a Special Edition of the Daily Phrophet questioning the safety of Hogwarts. If Sirius sees that, they are bound to have a picture of either Ron/Percy with Scabbers. You coukd also have Harry, unwilling for his new friends to get hurt, kill/severly injure him.

The same Special Edition could also suggest that Harry Potter was affected by the Killing Curse, and is himself on the path of becoming dark and therefore further outcasting him from his peers. Feeling alone, he may dedicate himself to magic and as such he begins to build a much larger spellbase.

The fact is, with such a simple thing a whole feild of oppurtunities arise which could affect the world.

 

Another location Hermione could die could be immediatly after ron gets hit, if the damage is more severe to his outer body, then Hermione might completely ignore Harrys warning of stopping and also get offed by the queen.

Then Harry's forced to struggle to survive against a chess set and loses the match and retreats backwards only to meet Dumbledore, and quirrel doesn't get a chance to get the stone.

 

Just because Luna doesn't act like a sycophant doesn't mean she doesn't think of Harry as a master though. There's more to having a henchgirl than goonery.

 

Luna for me, fills the "wiseman" roll better than Dumbledore does.

If you've read Unsung Hero, the later chapters have Luna acting as a "seer", where she assures Harry that good luck will come to him. Certainly, Luna is interesting because you can have her say ridiculous things and make her appear to be more than she is. She's a great foreshadowing tool. I can't see her becoming some puppet or goon of a dark wizard, however.

It's why I like Luna over Hermione. She's like "This is fact, I know it is. It is true,", while Luna is like "There is only one thing I know and it is that I know nothing,".