Itches to change principles (6)
I believe the answer is:
ethics
'principles' is the definition.
(ethic is a kind of principle)
'itches to change' is the wordplay.
'to change' indicates anagramming the letters.
'itches' with letters rearranged gives 'ETHICS'.
(Other definitions for ethics that I've seen before include "Codes of practice for businessmen" , "Some philosophy" , "Itches (anag)" , "Code of behaviour" , "Philosophical study of moral values" .)