Concession made by idiot after change of heart (3)
I believe the answer is:
sop
'concession' is the definition.
(I know that sop is a type of concession)
'by idiot after change of heart' is the wordplay.
'by idiot' becomes 'op' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'after' means one lot of letters go next to another.
'change' becomes 'ash' (ashing is a kind of changing).
'of heart' says to take the centre (I've seen 'heart of' mean this).
The central letter of 'ash' is 's'.
'op' after 's' is 'SOP'.
'made' is the link.
Can you help me to learn more?
(Other definitions for sop that I've seen before include "Concession made to pacify troublesome person" , "Propitiatory gift" , "Appeasing gift" , "A bribe or appeasement" , "usual way of doing things, initially" .)