Well while you can't change your chosen cantrips per se, you can learn new ones with scrolls assuming you can pay the gold it costs. IIRC it's 50 gold for cantrips, and it costs more as you increase the spell level. I believe this is limited to Wizards though.
Honestly, I am hoping that's a bug as DND 5e does not allow Wizards (or anyone else) to learn Cantrips from Scrolls - a cantrip is supposed to be a simple spell that you have mastered to a degree where it no longer consumes a spell slot to cast. Being able to learn it for 50g would indicate that you spend time writing it down in a spell book, which would make it a 1st level spell not a cantrip.
