Changeling/Oaths/Supernaturals

Can I just Fate-edit away an Oath with Fate Magic?

You can certainly try.

You will, however, fail in the end. While you may be able to shred the original Oath itself, one of the main themes of Changeling, of Fate magic, and of this specific game is that Fate always takes its price. The penalty for tearing apart an Oath witnessed by the Wyrd will always come home to roost, one way or another.