Notice only change (6)
I believe the answer is:
adjust
'change' is the definition.
(adjusting is a kind of changing)
'notice only' is the wordplay.
'notice' becomes 'ad'.
'only' becomes 'just' ('just' can be a synonym of 'only').
'ad'+'just'='ADJUST'
(Other definitions for adjust that I've seen before include "Adapt, fit" , "Alter by small amount to make right for use" , "Bring small change" , "Adapt, regulate" , "Alter, adapt" .)