Add new parts to, say (8)
I believe the answer is:
retrofit
'add new parts to say' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for retrofit that I've seen before include "Add (component) not originally in place" , "Later adjustment" , "Make later modifications to (equipment, etc)" , "Belatedly modify" , "Add (a component) not in the original build" .)