Did Harry being a Horcrux affect himself?

Question

In Harry Potter and the Order of the Phoenix (Ch. 22):

At once, Harry's scar burned white-hot, as though the old wound had burst open again - and unbidden, unwanted, but terrifyingly strong, there rose within Harry a hatred so powerful he felt, for that instant, he would like nothing better than to strike - to bite - to sink his fangs into the man before him.

This could mean 2 things:

• Either Harry was very angry and Lord Voldemort had successfully transferred his thoughts to kill Dumbledore for the moment. But given he wanted to sink his fangs, it is perhaps that Nagini did this.
• It might be a hyperbole that Harry was so angry with Dumbledore that he not only wanted to strike Dumbledore but give him a high degree of pain.

It seems like the first one has been considered as Dumbledore was careful enough not to be in direct contact with harry anytime. Only when Harry was in his office reporting Mr. Weasley's injuries, had this thought of harming Dumbledore happened. I don't know how Dumbledore noticed such a short though (Perhaps his skill in Legilimency?) but he did take notice and took extra precautions by asking Snape to teach Harry Occlumency.

This focus on the first point doesn't give any counter-proofs to the fact that Harry was a Horcrux and this might have affected him. As seen with the other Horcruxes, the person possessing the Horcrux has more affinity for darker thoughts. We sometimes see that Harry is overly moody and prone to rising temper. There are several incidents like what happened with Aunt Marge at 4PD or several times when he was at Hogwarts.

Is it mentioned somewhere how a living Horcrux affected the thoughts? Can somebody support or attack this statement with references.

Answer 1

The soul piece altered his thoughts only once.

JKR confirmed in an interview that when he looked at Dumbledore and felt something like a snake rear up inside of him, that was indeed Voldemort’s piece of soul stirring and moving in him. She further stated that the incident during his fifth year was the only time he felt it stir, and he was not contaminated or turned to an evil object by having the piece of soul living inside him.

JKR: And so this part of it flies off, and attaches to the only living thing in the room. A part of it flees in the very-close-to-death limbo state that Voldemort then goes on and exists in. I suppose it’s very close to being a Horcrux, but Harry did not become an evil object. He didn’t have curses upon him that the other Horcruxes had. He himself was not contaminated by carrying this bit of parasitic soul. The only time he ever felt it stirring and moving was in Order of the Phoenix, when he himself goes through a very dark time. And there’s a moment where he’s looking at Dumbledore, and he feels something rear like a snake inside him, and of course, at those times, it’s because the piece of soul inside him is feeding off his emotions. He’s going through a dark time, and that piece of soul is enjoying it, and making its presence felt, but he doesn’t know what he’s feeling, of course. Also, I always imagine that the Sorting Hat detected the presence of that piece of soul (JN: Yeah!) when Harry first tried it on, because it’s strongly tempted to put him in Slytherin. So that’s how I see it.
_{^{- PotterCast (Dec 23, 2007)}}

Though during that time in his fifth year, he did feel it and had thoughts caused by it, other than that his own thoughts were not changed by the soul piece.

It did affect him in other ways, though.

Though the soul piece did not turn his thoughts to evil except for the incident in his fifth year, Harry was affected by the soul piece in other ways. The pain in his scar was him feeling the pain of the soul piece trying to escape him and rejoin its master. It also caused his ability to occasionally see through Voldemort’s eyes and into his thoughts.

JKR: Well, of course the pain he feels whenever Voldemort’s particularly active is this piece of soul seeking to rejoin the master soul. When his scar is hurting him so much, that’s not scar tissue hurting him. That’s this piece of soul really wanting to get back out the way it entered. It really wants to- it entered this boy’s body through a wound, and it wants to rejoin the master. So when Voldemort’s near him, when he’s particularly active, this connection, (JN: Oh, my gosh!) it was always there. That’s what I always imagined this pain was. Yes, so there you go.
_{^{- PotterCast (Dec 23, 2007)}}

The soul piece did affect him, but by causing him pain when Voldemort was active and by connecting him to Voldemort so he could see through him and in his thoughts. When Voldemort was inactive, the only effect the soul piece had was giving him the ability to speak Parseltongue.