Makes changes to staler trash (6)
I believe the answer is:
alters
'makes changes to' is the definition.
(I've seen this in another clue)
'staler trash' is the wordplay.
'trash' indicates anagramming the letters.
'staler' anagrammed gives 'ALTERS'.
(Other definitions for alters that I've seen before include "Changes, modifies" , "Changes, makes different" , "Changes to staler state" .)