I left in changed form, such as Mr Hyde was known to do (10)
I believe the answer is:
mutilation
'as mr hyde was known to do' is the definition.
I can't judge whether this defines the answer.
'i left in changed form' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' indicates putting letters inside.
'changed form' becomes 'mutation' (I am not sure about this - if you are sure you should believe this answer much more).
'i'+'l'='il'
'il' going inside 'mutation' is 'MUTILATION'.
'such' is the link.
Can you help me to learn more?
(Another definition for mutilation that I've seen is " Dismemberment".)