Recognise and deny if it changes (8)
I believe the answer is:
identify
'recognise' is the definition.
(identifying is a kind of recognizing)
'deny if it changes' is the wordplay.
'changes' indicates anagramming the letters.
'deny'+'if'+'it'='denyifit'
'denyifit' is an anagram of 'IDENTIFY'.
'and' acts as a link.
(Other definitions for identify that I've seen before include "Establish who a person is" , "Sympathise" , "Discover name of" , "Give the name of" , "Recognise as specific person or thing" .)