Possible Clues:

• I'm not welcomed by a nameless child at a 20 centre first
• Any one of 17-, 24-, 50- or 59-Across
• Someone unacceptable in Rome - or anywhere else
• One banned each composition embodying new organ variation
• Reason NT paragon's upset? He's unwelcome
• Unwelcome one (... letters 5-11)
• After new performance nag opera star about drama queen's last part - one's not acceptable
• Pariah soon interrupts ditty beset by piano mistakes
• One who is not diplomatically acceptable
• According to boy, immediately cavorting at rag makes one out of favour