Matt rages after changing plan (9)
I believe the answer is:
stratagem
'plan' is the definition.
(I know that stratagem is a type of scheme)
'matt rages after changing' is the wordplay.
'after' is a charade indicator (letters next to each other).
'changing' indicates anagramming the letters.
'matt'+'rages'='mattrages'
'mattrages' anagrammed gives 'STRATAGEM'.
(Other definitions for stratagem that I've seen before include "Tag master with cunning plan" , "Start game with cunning plan" , "could be a trick" , "Crafty manoeuvre" , "way to outwit opponent" .)