Try changing horribly insane bully (9)
I believe the answer is:
tyrannise
'bully' is the definition.
(I've seen this before)
'try changing horribly insane' is the wordplay.
'changing' indicates anagramming the letters.
'horribly' indicates anagramming the letters.
'try' anagrammed gives 'tyr'.
'insane' with letters rearranged gives 'annise'.
'tyr'+'annise'='TYRANNISE'
(Other definitions for tyrannise that I've seen before include "Bully" , "oppression" .)