Change of home port -- miss a transformation (13)
I believe the answer is:
metamorphosis
'transformation' is the definition.
(metamorphosis is a kind of transformation)
'change of home port miss a' is the wordplay.
'change of' indicates an anagram.
'home'+'port'+'miss'+'a'='homeportmissa'
'homeportmissa' anagrammed gives 'METAMORPHOSIS'.
(Other definitions for metamorphosis that I've seen before include "Complete change of appearance" , "Total change in form" , "Process of transformation" , "changing?" , "Transmutation" .)