Changing train -- do it for practice (9)
I believe the answer is:
tradition
'practice' is the definition.
(tradition is a kind of practice)
'changing train do it' is the wordplay.
'changing' indicates anagramming the letters.
'train'+'do'+'it'='traindoit'
'traindoit' anagrammed gives 'TRADITION'.
'for' acts as a link.
(Other definitions for tradition that I've seen before include "Established practice" , "Custom, long-standing practice" , "Customs etc handed down" , "Routine" , "Beliefs, etc, handed down" .)