Feasibility of using Dark Magic to do a Horcrux-ectomy

Question

Based on this answer about what it takes to destroy a Horcrux, it seems that the key requirement is being damaged beyond magical repair (at least according to Hermione).

“Exactly,” said Hermione. “Our problem is that there are very few substances as destructive as basilisk venom, and they’re all dangerous to carry around with you. That’s a problem we’re going to have to solve, though, because ripping, smashing, or crushing a Horcrux won’t do the trick. You’ve got to put it beyond magical repair.”

_{Harry Potter and the Deathly Hallows, chapter 6: "The Ghoul in Pajamas"}

"Beyond magical repair" is a bit of a fuzzy limit, generally taken to mean Nagini (and by extension Harry) needed to die to destroy the Horcrux associated with them.

However, George Weasley's ear creates an interesting possibility, as it's cut off by Snape's Sectumsempra, and is explicitly beyond magical repair:

'I think so, although there's no chance of replacing his ear, not when it's been cursed off -'

_{Harry Potter and the Deathly Hallows chapter 5: "Fallen Warrior"}

Assuming a Dark Lord with a decidedly twisted sense of humor (and no common sense) snuck into the Burrow when George was a child and made that particular ear a Horcrux, it stands to reason that having the ear cursed off in that manner would put it beyond magical repair and destroy the Horcrux, leaving George both holey and Holy (at least in comparison).

Is there anything preventing the use of something like Sectumsempra to magic off the bit of Harry's forehead with the scar to get rid of the Horcrux?

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A note on J.K. Rowling: due to her unfortunate tendency to contradict herself, "Word of God" evidence rates lower than Cursed Child, which rates lower than Pottermore, which rates lower than the books.

I'll happily accept any evidence presented, as long as it's not contradicting something more trustworthy.

Answer 1

It might be possible, but living Horcruxes may work differently.

It seems theoretically possible that a living Horcrux could possibly be destroyed by cursing off a body part, unless a Horcrux in a living creature is sustained by the soul or life force so of its host wouldn’t be gone until the host is killed. The method of destroying a Horcrux that’s not alive is to put its object beyond magical repair, meaning do a certain amount of damage to the object in such a way that it can’t be repaired by magic (though it doesn’t have to be entirely destroyed).

“That’s a problem we’re going to have to solve, though, because ripping, smashing or crushing a Horcrux won’t do the trick. You’ve got to put it beyond magical repair.”
_{^{- Harry Potter and the Deathly Hallows, Chapter 6 (The Ghoul in Pyjamas)}}

It has to be something powerful enough that the Horcrux can’t simply repair itself magically.

“It doesn’t have to be a Basilisk fang,’ said Hermione patiently. ‘It has to be something so destructive that the Horcrux can’t repair itself.”
_{^{- Harry Potter and the Deathly Hallows, Chapter 6 (The Ghoul in Pyjamas)}}

Having a body part cursed off by Dark Magic is irreparable by magic, so it seems like it might count.

“Mrs Weasley looked round and said, ‘I can’t make it grow back, not when it’s been removed by Dark Magic. But it could have been so much worse … he’s alive.”
_{^{- Harry Potter and the Deathly Hallows, Chapter 5 (Fallen Warrior)}}

Though it’s not as drastic as dying, it is damage beyond magical repair, and so theoretically it might work. However, it may be different in the case of a living Horcrux. It’s possible that with a living Horcrux, the piece of soul is sustained by the “host” soul, and that soul or life force needs to be killed before the Horcrux can be destroyed. Another problem with the idea that the piece of soul in Harry could be killed by just cursing off a part of him is that although Dumbledore suspected Harry had it in him for a while (so he had time to think) and he would have rather kept Harry alive, he never tried cursing off a body part before deciding Harry had to die.

The piece of soul itself doesn’t seem to exist in any specific spot.

Though his scar was certainly connected to the piece of soul in him, in general, Horcruxes don’t seem to have the piece of soul exist in one specific place within them. It didn’t seem to matter where any of the Dark Lord’s Horcruxes were damaged beyond magical repair, just that they were. It also doesn’t seem in any way possible when creating a Horcrux from a living being to use a specific body part to house the soul piece. It most likely can’t be placed specifically in an ear.

Answer 2

I don't think this is answerable, because there are no canonical examples of a Horcrux of the type "George Weasley's ear". I somewhat doubt that you could even make an ear that is attached to a body into a Horcrux. There are a number of weird issues that would come up if it's possible to make a Horcrux out of something other than a single discrete, complete object or entity.

Horcruxes that are living beings

The situation with Harry and Nagini seems to be that the living being itself is the host for the soul fragment; it isn’t connected to one particular part of their bodies as far as I can tell. Harry's scar was created when the soul fragment entered him, and it seems to serve as a locus for Harry's special Voldemort-related senses, but it seems very doubtful to me that anything but the death of the living being that contains the soul fragment would count as sufficient damage to destroy the Horcrux. Evidence:

• Hermione makes it clear that in a conventional Horcrux, the soul fragment is dependent in some way on the physical integrity of its vessel (hence her somewhat confusing statement that "a Horcrux is the complete opposite of a human being"). But the soul fragment in Harry is destroyed when Voldemort Avada Kedavra’s him; we know that AK normally doesn’t do any damage to the body (there are various descriptions of this fact; e.g. at the start of Book 4). It seems therefore that the soul fragment in Harry is somehow tethered to this world by Harry's life.

• Harry is a vessel for Voldemort’s soul fragment despite having a scar on his forehead that cannot be healed because it was caused by Dark magic. (I’m not sure if the scars he gets from Umbridge’s pen would also count as Dark magic wounds.)

• When Harry asks Dumbledore if it is risky to make a living being into a Horcrux, Dumbledore brings up the risk of entrusting part of your soul to something that can think independently of yourself; he doesn't say something like "yes, it's risky because living beings can be permanently scarred by Dark magic, which would destroy the soul fragment even if the living being survived".

• Likewise, Dumbledore tells Snape that Harry must die; he doesn't say "or, we could cut off part of the skin on his forehead".

• Dumbledore says "You were the seventh Horcrux, Harry, the Horcrux he never meant to make" (Harry Potter and the Deathly Hallows, Chapter 35). It's true that Dumbledore's wording here is not particularly precise, since JKR has clarified that Harry was not strictly speaking a Horcrux going by the technical definition of that term (which refers to something that has been intentionally made into a soul container by the use of some kind of Dark magic--what the Harry Potter wiki calls the "Horcrux-making spell"). But nevertheless, it seems relevant that Dumbledore says that Harry, himself, acts as the seventh Horcrux. He doesn't say "Your scar is the seventh Horcrux."