If they knew the place was compromised with Snape knowing its location and the Order thinking him a traitor, why didn't someone just remove and recast the Charm? Obviously, we know that he didn't tell the Death Eaters. The idea that how to cast the Charm isn't widely known doesn't hold weight either as someone within the Order cast the Charm on Shell Cottage. Unless they specifically had to learn it for that, but at the same time, the same logic applies, why didn't they just do that for Grimmauld Place?

For that matter, a Fanfic that I read that was released after HBP figured the idea out. Even if it was going on the original logic that if the Secret Keeper (or the caster, can't remember which.) dies, the Charm cancels out. I guess that Hermione was right, Wizards really don't use Logic a lot do they? But I'm surprised that Hermione didn't come up with the idea herself for that matter.

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    As Hermione said at the end of PS, wizards aren't exactly known for their logical skillz – user13267 Nov 20 '18 at 11:24
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    There's nothing in the seven books that indicates that you can reverse the Fidelius charm. – Anthony Grist Nov 20 '18 at 13:40
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    Presumably because the original Fidelius Charm was still in place. There's nothing which indicates that you can layer Fidelius Charms in any effective way. Additionally, when first describing the Charm Flitwick indicates that it's a rare and powerful charm. Not the sort of thing that can be casually reperformed when your Secret Keeper dies. – The Dark Lord Nov 30 '18 at 0:38
  • I closed this as a duplicate of the linked question as it seems to be asking the same thing. If it’s not, feel free to edit your question to clarify the difference(s). – Alex May 12 '19 at 14:48

I just noticed the wording on the quote about the Fidelius charm from PoA, it specifically mentions soul, which as we know is a big part of the "magic system".

An immensely complex spell involving the magical concealment of a secret inside a single, living soul. The information is hidden inside the chosen person, or Secret-Keeper, and is henceforth impossible to find — unless, of course, the Secret-Keeper chooses to divulge it. As long as the Secret-Keeper refused to speak, You-Know-Who could search the village where Lily and James were staying for years and never find them, not even if he had his nose pressed against their sitting room window!" —Filius Flitwick explaining the charm

in the context of creating a Horcrux, or avada kedavra, magic that interacts with the soul seems fairly permanent, especially from Voldemort's experience of being hit by the killing curse, his soul is ripped from his body, and is only protected by the existence of the Horcrux's, and returned to the body by powerful dark magic.

“I was ripped from my body, I was less than spirit, less than the meanest ghost . . . but still, I was alive.”

― Voldemort, Harry Potter and the Goblet of Fire

I believe for this reason, the removal of the Fidelius charm would have been immensely damaging to the soul that kept the secret, and in the event of the death of Dumbledore, I speculate that the action would have needed to be performed on each of the new secret keepers.

Also as others have mentioned, there is no reference to the removal of the charm throughout the books, and I doubt it would have even been attempted, or created as a spell.

As we can see from most other spells from the universe, a lot of spells do not have a reversal i.e Lumos and Nox, however they have counter magic/spells, or magic/spells to fix the damage, and in this case, I'd guess the reversal is just not possible.

Hope this answers your question.

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