Go to have a fight, showing change of mind
I believe the answer is:
turnabout
'change of mind' is the definition.
('turnabout' can be a synonym of 'change of mind')
'go to have a fight' is the wordplay.
'go' becomes 'turn' ('turn' can be a synonym of 'go'**).
'to have' means one lot of letters go next to another.
'fight' becomes 'bout' ('bout' can be a synonym of 'fight').
'turn'+'a'+'bout'='TURNABOUT'
'showing' acts as a link.
(Other definitions for turnabout that I've seen before include "That makes a change" , "change of heart" , "Total change of policy" , "complete change of policy" .)