Change people appearing in advertisement (5)
I believe the answer is:
amend
'change' is the definition.
(I know that amend is a more specific form of the action correct)
'people appearing in advertisement' is the wordplay.
'people' becomes 'men' (men are people).
'appearing in' is an insertion indicator.
'advertisement' becomes 'ad' (short for advert).
'men' placed within 'ad' is 'AMEND'.
(Other definitions for amend that I've seen before include "Correct error, make minor alteration as to writing" , "Corrct error, make a minor aleration" , "Modify, correct" , "Make small improvements to" , "Make minor improvements to (something)" .)