The Wiener Staatsoper has announced cast changes for its productions of “Le Nozze di Figaro” and “Don Giovanni.” First, the company said that Federica Lombardi will sing the Countess in “Le Nozze di Figaro” on Oct. 2 stepping in for Hanna-Elisabeth Müller. Secondly, the company said that Oleg Ptashnikov will conduct the October performances of “Don Giovanni” stepping in for {…}