Complex sentence: He pleaded with Malko to be accepted on a provisional basis, and over the years in fact became the supreme authority on manual technique, having developed a system, which he expounded in his book "The Technique of Conducting".
Split into simpler sentences: He pleaded with Malko to be accepted on a provisional basis. Over the years Musin actually became the supreme authority on manual technique, expounding upon his system in his book "The Technique of Conducting".