Complex sentence: Otto's election and coronation took place in the right places, namely in Cologne and Aachen, and his coronation was carried out by the Archbishop of Cologne, but only with a substituted set of regalia.
Split into simpler sentences: Otto's election and coronation took place in the right places, namely in Cologne and Aachen. In addition his coronation was carried out by the Archbishop of Cologne, but only with a substituted set of regalia.