Smoother MP is a refined change (13)
I believe the answer is:
metamorphosis
'change' is the definition.
(I've seen this before)
'smoother mp is a refined' is the wordplay.
'refined' indicates an anagram.
'smoother'+'mp'+'is'+'a'='smoothermpisa'
'smoothermpisa' with letters rearranged gives 'METAMORPHOSIS'.
(Other definitions for metamorphosis that I've seen before include "Transmutation" , "changing?" , "Total change in character" , "Total change in form" , "Complete change of appearance" .)