Break down changing lane, say (7)
I believe the answer is:
analyse
'break down' is the definition.
('analyse' can be a synonym of 'break down')
'changing lane say' is the wordplay.
'changing' indicates anagramming the letters.
'lane'+'say'='lanesay'
'lanesay' with letters rearranged gives 'ANALYSE'.
(Other definitions for analyse that I've seen before include "Break down into components parts and examine" , "Sort out syntax" , "Examine and interpret" , "Dissect" , "Any seal (anag.)" .)