A relatively short (only a bit over 1,000 words) explanation of why Celestia removing Twilight's mark and horn is either nearly impossible or just a stupid idea

(in response to this thing that was made over 2 years ago: https://derpibooru.org/92619?scope=scpe1f425e264717a35ab792fc080dc8db7c30a72b44)

You know, I just realized how stupid this idea of a story would be. She's the element of magic, she's been trained in magic since she was young, and I'm fairly certain Celestia doesn't have the power to remove a cutie mark and a horn from a long distance and transform a pony into an earth pony. This would mean completely changing them to be able to use Earth Pony magic if they learn how, unless some magical surge occurs, because completely changing the genetic makeup of a living and making the cutie mark vanish would be a huge waste of energy, and the skill to do so at a long distance while blocked off by walls requires immense skill, care, and energy.

This is because the process of changing the genetic makeup of a living being without causing hideous mutations or cancer or just straight up failing and killing the one your trying to, really, mutate would have to be careful and require skill and time to complete without botching it up to the point where it's irreversible, they're laden with cancer, or they can't function normally.

And then, when it's over, the whole process would have to be reversed, something that may be harder or easier than the initial change, given the changes, but it would require the horn to be regrown entirely, sapping quite a bit of energy, nutrients, and minerals from the one growing it as cells replicate at an abnormally high rate, meaning she'd have to be eating extra before, during and after this to replenish the nutrients, material, and energy required to cause such a quick growth, which would have to grow even faster than cancer.

Since it normally takes 20-22 hours for cells to replicate, though it may take longer for ponies because we have only 23 chromosome pairs (46 chromosomes) while equines have 31 pairs (62 chromosomes) and then the extra chromosomes that would be related to the use and type of magic and the wings/horn, which would require at least 1 extra gene pair, if not more. All of those must replicate during interphase's S phase and be checked in G2 before replicating in Mitosis, not to mention how the cells have to grow in G1 and replicate the Organelles inside the cell before S and G2, all of which must occur before before M phase, Mitosis, where the cells actually duplicate.

You can't really shorten the process unless you feel like skipping G2, something not even Cancerous cells skip, and then without G2, there isn't any checking to see if your genes are damaged in some way and no attempt to fix it, meaning there's a higher chance of having horrible mutations or just dead cells as a result of duplication, which would be a waste of time, energy, and materials, just like cancer except it won't even replicate.

If you say that the horn is stuck in some magical stasis and it will reattach it once Celestia thinks she's suffered enough going against her true nature, instinct, and literally what fate ordained to be her purpose, to use magic, there's still the little matter of how Celestia is able to precisely remove it without damage or bleeding while changing her genetic makeup to that of an Earth Pony from Canterlot while she's in Ponyville. Then, there's how she'll change he back to a Unicorn on the genetic level while fusing her horn to allow her to use magic without botching up the re-attachment, re-connection of blood vessels, re-connection of nerves, and the re-connection of the ability to channel magic through the horn.

Then, there's how she removed her cutie mark. If she's able to do that, then likely she either spent time developing it and practicing it, perhaps as a form of punishment or mental torture for some, or some pony in the past created the spell and Celestia not remove that spell from the public eye, but also learned it and will casually use it because someone does what the their cutie mark indicates that they should do. If course, this means she should remove her cutie mark due to her work with the sun and remove her horn because of how she uses it a lot, for things ranging from sipping tea to moving the sun to doing this, or else she's a hypocrite. Oh, and she should remove Applejack's mark because she farms apples, Luna's mark because she moves the moon, the marks of the flower farmers because they farm flowers, the mark of literally everyone that follows their mark because they like to do and use what their mark ordained.

Not only that, but how did she remove something ordained by fate to appear without replacing it? Not even Starlight Glimmer could do that, she could only remove the mark and replace it with an inferior mark. It should not be possible.

And along with that, remember the episode with the hydra, when she tried to jump across instead of just teleporting like she so casually does when it's unnecessary like in Canterlot when singing about her test? She doesn't use magic for everything, and if Celestia really wanted to force Twilight to not use magic without forcing me to write about why her actions are extremely hard to do, she could stick an inhibitor ring on her. You know, the ring that shuts off a Unicorn's ability to use magic and then binds itself so the wearer can't take it off?

TL,DR: her actions require too much energy and materials, changing the genetic makeup of a living being without inciting horrible mutations and cancer is practically impossible, especially from a distance, reattaching the horn is hard, though not as hard regrowing it, which would be akin to forcing something slightly worse than cancer on the subject and then shutting it off at will and somehow not having any genetic errs in the horn's cells, her removing only Twilight's horn and mark is not only horrifying but hypocritical as she does it to only Twilight and not literally every pony that follows their mark or does what their race is good at, Twilight already didn't use magic for everything, and it would be far easier to use an inhibitor ring to prevent magic use.