Perhaps you do not see Christ in Isaiah 53.
I strongly doubt He would ever change "the original terms" He had with Israel.
God didn't "change the original terms." He did what He said He would do -- He sent them a Savior, "bruised for their transgressions."
But this theological distinction seems intent on side-tracking the thread. Let's stay focused on the pope's global authority "with teeth" (and the means to coerce) which the pope is advocating.
I have already given a "backgrounder" on the "with teeth" episode.
I gather you were not at all persuaded by it.