My understanding was that the swapping of the cutie marks was a symptom of what was going on, rather than the entirity of what was happening. The marks represent many things about a pony. Their passion, their talent, and sometimes it's just a representation of the event that led to the epiphany about what they want to do (that latter was the case for, like, four of the main six). Rarity's cutie mark is a set of gems, because the incident with the gemstones was what cemented her belief that dressmaking
was her calling, when before she had been starting to doubt that. Just like how with Fluttershy, it was being caught by those butterflies that led to her big Disney Princess revelation.
My belief is that the Unfinished Spell didn't directly change their marks, but rather changed something fundamental about them, exchanging certain memories, personality traits, and such. They all seemed convinced that this is what they were meant to do, and what they had
always known they were meant to do. And the cutie marks shifted to match that, even when the meaning of the mark is lost on its new owner. I think it's actually kinda meaningful that the meaning of, say, Rarity's mark is totally lost on Applejack. Outside the context in which it was received, it wouldn't make a lot of sense.
The Elements, too, I think were just a symptom. They were also a focus for the magic, since each one is attuned deeply to its user. They're connected. Each one took on the shape of their cutie marks after they were each revealed to be the element's new bearer. As such, when the spell changed who they each are, the elements responded in kind.
The characters' real selves were still there, but buried under the new traits that were being imposed on them. Repairing them required what was essentially a forced repeat epiphany.
edited 18th Feb '13 8:35:32 AM by Enlong
I have a message from another time...