Alter shape afterwards (5)
I believe the answer is:
later
'afterwards' is the definition.
('later' can be a synonym of 'afterwards')
'alter shape' is the wordplay.
'shape' indicates an anagram.
'alter' is an anagram of 'LATER'.
(Other definitions for later that I've seen before include "after the rest?" , "Afterward, subsequent" , "Alert (anag.)" , "At a time in the future" , "Alter (anag.)" .)