A page in old hat getting changed (7)
I believe the answer is:
adapted
'changed' is the definition.
(adapting is a kind of changing)
'a page in old hat' is the wordplay.
'page' becomes 'p'.
'in' indicates putting letters inside.
'old hat' becomes 'dated' (I've seen this before).
'p' put inside 'dated' is 'dapted'.
'a'+'dapted'='ADAPTED'
'getting' acts as a link.
(Other definitions for adapted that I've seen before include "made to fit" , "Changed to suit anoter purpose" , "Became adjusted" , "Changed for a particular purpose" , "Adjusted to new conditions" .)