Possible Clues:

• Rule out piece of Chopin, say, covering his head
• Rule out what's initially captured in introduction
• Stop killjoy touring European capital after vacation
• Rule out C found in musical work
• Prevent Chopin initially plugging one of his compositions?
• Rule out report of how lazy compiler acquired crossword?
• Rule out overture to include music finale
• Bar in park is about to open for dinner - it's in guide that appeals to cruciverbalists
• Rule out solution already hinted at when editor returned
• Make it impossible to get the key into the opening