Clue: Production of Tosca includes beginning once rendered dissonant (8)
Answer: SCORDATO
Explanation: Definition: dissonant
***(tosca)** *includes* **O**(nce) **R**(endered) **D**(issonant) 
*"Dissonant" seems to be doing double duty here unless Azed intends this to be & lit. My knowledge of classical music doesn't extend far enough to know whether the beginning of Tosca is considered to be disssonant.