Roughly back in charge of modified car (5)
I believe the answer is:
circa
'roughly' is the definition.
(I've seen this before)
'back in charge of modified car' is the wordplay.
'back' says the letters should be written backwards.
'in charge of' becomes 'ic'.
'modified' indicates anagramming the letters.
'ic' written backwards gives 'ci'.
'car' is an anagram of 'rca'.
'ci'+'rca'='CIRCA'
(Other definitions for circa that I've seen before include "Approximately, around" , "Approximately (Latin)" , "Roughly" , "Close to" , "Preceding a date, this means about" .)