Composer has new role as single man (8)
I believe the answer is:
bachelor
'single man' is the definition.
(unmarried man)
'composer has new role' is the wordplay.
'composer' becomes 'bach' (Johann Sebastian Bach).
'has' means one lot of letters go next to another.
'new' indicates an anagram.
'role' anagrammed gives 'elor'.
'bach'+'elor'='BACHELOR'
'as' acts as a link.
(Other definitions for bachelor that I've seen before include "Unmarried man (with a degree?)" , "Graduate" , "Unmarried male" , "leading man at start of Wedding Cantata" , "He's not married" .)