Complex sentence: In fact, he soon becomes the head of the Cappella Giulia again, and, as the first and only musician, receives the title of composer of the Cappella Pontificia "modulator pontificus".
Split into simpler sentences: In fact, he soon became the head of the Cappella Giulia. And he was the first and only musician to receive the title of composer of the Cappella Pontificia "modulator pontificus".