If you are Protestant — if you don’t believe in an infallible/one true church, and as a separate church you were founded by a schism from your lawful ecclesiastical head, you have no right to invoke Nicæa. Ever.Well, bullshit. My lawful head, the only Head the church has, is Jesus. And I never swore fealty to either Rome or Constantinople; if indeed I owe such an utter debt of loyalty to any earthly church, it would be to 815 2nd Avenue, for it was a Episcopal bishop who confirmed me.
Looking at Nicea as a simply a matter of legal authority is not the only possibility, and it is not the possibility that has any relationship to truth. Nicea's most tenacious authority doesn't come from its political relationship to any bishop, but from its repeated, persistent ratification by generations of theologians coming from a variety of theological approaches.