Don't change it round! Composer in the end kept faster pieces of music (7)
I believe the answer is:
stretti
'pieces of music' is the definition.
(I've seen this before)
'don't change it round composer in the end kept' is the wordplay.
'don't change' becomes 'stet' (publishing term).
'round' is an anagram indicator.
'in the end' says to take the final letters.
'kept' means one lot of letters goes inside another.
The final letter of 'composer' is 'r'.
'it' with letters rearranged gives 'ti'.
'stet'+'ti'='stetti'
'stetti' going around 'r' is 'STRETTI'.
'faster' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stretti that I've seen before include "musical pieces" , "Musical passages" , "Pieces of music" , "fugal devices" .)