Green satin cover is not to be changed (15)
I believe the answer is:
conservationist
'green' is the definition.
(thesaurus)
'satin cover is not to be changed' is the wordplay.
'to be changed' indicates anagramming the letters.
'satin'+'cover'+'is'+'not'='satincoverisnot'
'satincoverisnot' with letters rearranged gives 'CONSERVATIONIST'.
(Other definitions for conservationist that I've seen before include "One preserving the environment and wildlife" , "One who preserves and repairs significant artefacts" , "Protector of environment" .)