What are the chances your favorite pony was secretly a changeling all along?

Yeah, probably about one in one.

Applejack is chosen as The Nightmare's new host.

It really isn't that big of a deal. Until it is.

While researching a new spell, a miscalculation leads to Twilight and Pinkie Pie switching bodies. They decide to hide the accident and live as one another - for Science! What could possibly go wrong?
(With apology to the scientific method)
Cover art by Conicer!

Scootaloo overhears Twilight talking about a time travel machine. She breaks into the library and travels back in time to meet her hero, Rainbow Dash, as a filly. It would have been the perfect plan if Dash had been anything like she expected.

Story prompt/Requested by: TheDarkPrep
Edited by: Selbi, Abcron
Part of my one-shot week.

Twilight wakes up one morning to find herself in the body of a filly she doesn't recognise. And it seems like she's not the only one...