Change the appearance of flag, not new (8)
I believe the answer is:
redesign
'change' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for redesign that I've seen before include "New look" , "Draw or plan again" , "Modernise" , "Make new plans" , "Plan something again" .)