This episode is the first time cutie marks were intentionally switched or rearranged between ponies. Last time such a thing happened, it was accidentally done by Twilight Sparkle.
Counting Applejack (as a baby), Rainbow Dash, Pinkie Pie and Fluttershy's cameos in dream bubbles and excluding Rarity in the stain glass window, this is the first episode since "Luna Eclipse" where Rarity is the only Mane Six member (and the only main character altogether) to be absent.