Changed modus operandi and failed to protect single female (8)
I believe the answer is:
modified
'changed' is the definition.
(modifying is a kind of changing)
'modus operandi and failed to protect single female' is the wordplay.
'modus operandi' becomes 'mo' (common abbreviation).
'and' is a charade indicator (letters next to each other).
'failed' becomes 'died' ('die' can be a synonym of 'fail').
'to protect' is an insertion indicator.
'single female' becomes 'if' (I can't justify this - if you can you should believe this answer much more).
'died' enclosing 'if' is 'dified'.
'mo'+'dified'='MODIFIED'
Can you help me to learn more?
(Other definitions for modified that I've seen before include "Made minor changes to" , "Altered, changed" , "Altered, qualified" , "tweaked" , "Changed slightly, form or quality" .)