Possible Clues:

• Theatrical organiser
• A promise I broke around first of rules -- fair boss?
• Showman, one taking Paris and Rome by storm?
• Theatre promoter
• Mostly have big effect on a carnival site as stage manager
• Concert master
• As a showman, one eccentric is Mr Opera!
• Author's praise, or otherwise, for manager
• 'The --', an operetta by Mozart
• One organising 21 had this in Oldham