Complex sentence: When not touring with Blondie, he performs as a guitarist in the fictional 1980's Rock Band Arsenal in the Broadway musical, Rock of Ages, a member since it opened off Broadway in 2008.
Split into simpler sentences: When not touring with Blondie, he performs as a guitarist in the fictional 1980's Rock Band Arsenal in the Broadway musical, Rock of Ages. He has been with Rock of Ages since it opened off Broadway in 2008.