What if two mares of great magic had been born in each other's towns?
Twilight Sparkle in Hoofington, and The Great and Powerful Trixie in Canterlot?
Would that change their destiny?

Brought up in the rich and high-class city of Canterlot, Trixie had all life could offer. When her magic began to blossom, her parents did everything they could to make sure she got into Celestia's Private School for Gifted Unicorns. Out of sheer pride, Trixie knew she had to pass that entrance exam and make her parents proud.
Unlike the test of the Dragon Egg that is posed to students who have already been accepted into the school, the test posed to Trixie was to lift a Phoenix feather a foot into the air. This test is actually much more difficult than it sounds, as it requires perfect control and power to lift such a magical item.
After struggling with the feather for almost an hour, Trixie was about to give up when a crashing boom ricocheted across the sky, and startled her into awaking power she didn't know she had, causing her to not only lift the feather far into the air, but also imbue it with life and create a newborn phoenix. As the instructors dived for cover from the brilliant blue flames that were beginning to surge, a red phoenix could be seen winging off towards the Solar Tower.
Before any lasting damage could be done, Celestia arrives to calm the awoken magic, and take the young filly under her wing as her personal student.

So it seems that destiny has indeed changed... But will the change of two fillies' paths change the path of a black Alicorn's as well?