How Alicorn Twilight fits into my head-canon

*I’ll be referring to my multi-dimensional backstory “The Eternal Conflict” throughout this piece. Though I will recap the points that are relevant to this piece, if you want to get the whole story, I recommend checking that out before reading this.*

This is my explanation as to how Alicorn Twilight fits in with my personal head-canon about the alicorns.
For starters, a short recap of what the alicorns (specifically Princess Celestia and Princess Luna) are to me: They are beings created from the pure essence of harmony from a separate dimension. Outside of this dimension, such purity cannot be maintained. This explains why the Elements of Harmony – which contains the pure essence of harmony that the alicorns are made from – had to be separated into the six elements we know of today. It also explains why Princess Luna was able to be corrupted by the Miasma and transformed into Nightmare Moon.
With Twilight being turned into an alicorn, this appears to disagree with my head-canon. After all, Twilight certainly isn’t a being born of the pure essence of harmony; she was a unicorn born in Equestria. This can work, however; I’ll explain.
Before Twilight was turned into an alicorn, she was transported to a strange location, where Princess Celestia eventually transforms her into an alicorn. This location certainly has the appearance of some sort of ethereal dimension, separate from Equestria, so let’s assume that’s exactly what it is. This pocket dimension acts as a waypoint between the world where Equestria exists and the alicorn’s home dimension. Here, Princess Celestia is able to infuse Twilight with some of the pure essence of harmony, transforming her into an alicorn – or, at least something that looks like an alicorn.
You see, I never really mentioned it before  though I sort of inferred it with the spirits of The Great Darkness – but because they are beings of pure essence, the creatures of that dimension have no need for physical bodies within their home dimension. They are only required to take a physical form upon leaving that dimension. So it stands to reason that the alicorn’s form was designed to look similar to the creatures they decided to look after. This would be especially true when Princess Celestia and Princess Luna decided to live among their wards.
Anyway, when Twilight became infused with the essence of harmony (remember, the purity couldn’t be maintained outside the home dimension), one of two things could have happened:
The essence could have overwritten her body and actually transformed her into an alicorn, or
The essence simply altered her form and gave her the appearance of an alicorn.
I’m more inclined to believe the second option, as I’d be hard-pressed to believe that any lesser being could be transformed into being that’s created from a pure essence – even when that purity is compromised.
The fact is, we don’t know how much Twilight’s being has changed; all we know is that she has a pair of wings now – a physical transformation, nothing more (though we can probably assume that she can interact with clouds, like a pegasus can). Until we see more of her, we won’t know how deep the infused essence transformed her.
Now, as I thought about this topic, another question popped into my head: What about Princess Cadence? Where does she fit into this? Originally, I thought there wasn’t much I could with her, as we didn’t know anything about her past (besides her connection with Twilight). However, I was reminded that that’s no longer true; the chapter book Twilight Sparkle and the Crystal Heart Spell provides Cadence’s backstory. It shows that Cadence was originally a pegasus and that – after completing a particularly monumental feat – she was transported to Celestia’s pocket dimension and was transformed into an alicorn – just like Twilight. With Cadence, we do get some sense as to how the transformation actually changed her; after all, she was originally a pegasus, but now wields magic as well as any unicorn (probably more, considering the effect she achieved when augmenting Shining Armor’s magic). If the essence transformation is capable of giving a pegasus magical capabilities, we can only imagine what it will do to Twilight, a unicorn that already had potent magic abilities.