I agree with @rand al'thor. Harry is definitely not a horcrux. Although I'm sure your reason from this Rowling person is fine, I have a different reason for this belief.
First, I would like to clear up that a Horcrux is defined as a piece of someone's soul attached to an object, as Slughorn says:
"A Horcrux is a word used for an object in which a person has concealed part of their soul."
That's an object. Not anything else. Living Horcruxes are possible, like Nagini, but for them, the soul is a Horcrux--attached to the body--the object. Whereas in Harry's case, the fragment of Voldemort's soul is fixed to his soul, not his body, just like Dumbledore says:
"...on the night Lord Voldemort tried to kill him, when Lily cast her own life between them as a shield, the Killing Curse rebounded on Lord Voldemort, and a fragment of Voldemort's soul was blasted apart from the whole, and latched itself onto the only living soul left in the collapsing building.
So the fragment of Voldemort's soul is attached to Harry's soul, not his body. He is not a Horcrux.
To answer your question, the Horcrux defense mechanism will therefore activate only if harm comes to the soul, like Avada Kedavra or something. If harm comes only to the body, the soul is unharmed.
"Look, if I picked up a sword right now, Ron, and ran you through with it, I wouldn't damage your soul at all...whatever happens to your body, your soul will survive, untouched."
Thanks to Hermione, we can conclude that whatever physical harm comes to their body from any spells you may be thinking of, the soul will be fine, and therefore the Horcrux mechanism will not trigger.