Fitting in' dead wrong, so changed (7)
I believe the answer is:
adapted
'changed' is the definition.
(adapting is a kind of changing)
'fitting in' dead wrong' is the wordplay.
'fitting' becomes 'apt' (both mean appropriate).
'in'' means one lot of letters goes inside another.
'wrong' indicates an anagram.
'dead' is an anagram of 'aded'.
'apt' put inside 'aded' is 'ADAPTED'.
'so' is the link.
(Other definitions for adapted that I've seen before include "Became adjusted" , "Altered" , "Date-pad (anag.)" , "Made suitable for new purpose" , "Modified to suit" .)