From a reader…
I know Cardinals can celebrate pontifical high masses “at the throne” anywhere. Can metropolitan archbishops do so anywhere within the ecclesiastical province, or only within their own archdiocese?
According to the Usus Antiquior, the Extraordinary Form – call it what you will so long as you use it – the Metropolitan may celebrate a Pontifical Mass at the Throne anywhere within the territory of his province.
He would normally not do so without informing the suffragan, the local bishop, out of respect. You don’t just barge into to another bishop’s diocese and start doing things.
You can find answers to questions such as these in Alcuin Reid’s reworking of Ceremonies of the Roman Rite Described.