If you are looking for spellcaster-caliber Fate magic, then the Sponsored Magic option is likely the way to go. However, since you mentioned the idea of a power that was largely aspect-based ... you might want to look at the "Blessed Words" stunt (example on YS378).
A possibly better/more flexible way would be to re-skin Incite Emotion (ie, Incite Fate). At the -1 base price, I would suggest only allowing the power to govern 'negative' fate aspects to parallel the amount of utility the base power grants. So basically, this would allow you to 'curse' someone's fate on the short term. If you want it to be able to govern positive tweaks to fate, as well, then I'd consider upping that to -2.
Looking at the costs, you get the following:
-1 Fated Words: As Blessed Words, but lays a scene aspect relating to fate.
-1 Curse Fate: As Incite Emotion, but with fate-based curse aspects.
-2 Incite Fate: As Incite Emotion, but with positive and negative fate-based maneuvers.
-2 Channel (or Ritual) Fate: As Channeling or Ritual (pick one, or buy both) using fate as the element/theme. (Note that while this is more flexible than Incite for the same refresh, Incite is 'free' to use.)
-4 Fate Magic: Sponsored Magic granting both Channeling and Ritual Fate, with Rituals cast as Evocation.
One other thing to consider. Is fate-based magic Lawbreaking? I'm not sure. Consider:
Thaumaturgy that fundamentally, lastingly changes the target—whether it’s the target’s body, mind, emotions, or even luck—falls into the category of transformation and disruption. Often, this is dark stuff—curses, mind control, destructive shapeshifting, and death magic.
Of all the methods available through thaumaturgy, these are the ones most prone to run afoul of the Laws of Magic
Certainly not conclusive, and you might argue that you aren't changing the
person so much as the universe surrounding him. But that's something the Table should discuss.