Bully to use tribal form (9)
I believe the answer is:
brutalise
'form' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'bully to use tribal' is the wordplay.
'bully' indicates an anagram (I've seen this in other clues).
'use'+'tribal'='usetribal'
'usetribal' anagrammed gives 'BRUTALISE'.
Can you help me to learn more?
(Another definition for brutalise that I've seen is " Make bestial".)