The earliest I was able to find, based off Bulbapedia's list of ways to change Abilities, was Sylveon. Pick up an Eevee from Route 4's grass, evolve it as soon as you get it, and level the Sylveon up to Level 25. This is when it learns Skill Swap, which is the earliest possible way to get a move like this -- barring trading, inconvenient breeding, and grotesque overlevelling. For reference, Level 25 should put you around Olivia in terms of game progression.
You can also SOS chain for a Power of Alchemy Grimer-Alola at the Trainer's School, but I doubt you want to know what Abilities your party Pokemon have.