Again change a physical exercise after study (7)
I believe the answer is:
readapt
'again change' is the definition.
('adapt' is an answer for 'change' so perhaps 'readapt' is OK for 'again change')
'a physical exercise after study' is the wordplay.
'physical exercise' becomes 'PT' (Physical Training).
'after' says to put letters next to each other.
'study' becomes 'read' (synonyms).
'a'+'pt'='apt'
'apt' after 'read' is 'READAPT'.
(Other definitions for readapt that I've seen before include "Once again modify" , "again demonstrate versatility" , "undergo further change" , "Again adjust to changed conditions" , "make further modifications" .)