Piece of music Verdi arranged, with tempo not changed (12)
I believe the answer is:
divertimento
'piece of music' is the definition.
(divertimento is a kind of piece of music)
'verdi arranged with tempo not changed' is the wordplay.
'arranged' is an anagram indicator.
'with' is an insertion indicator.
'tempo' becomes 'time' (I've seen this before**).
'changed' indicates an anagram.
'not' with letters rearranged gives 'nto'.
'time' put within 'nto' is 'timento'.
'verdi' with letters rearranged gives 'diver'.
'diver'+'timento'='DIVERTIMENTO'
(Other definitions for divertimento that I've seen before include "Light orchestral work" , "Light musical piece" , "Piece of music" .)