Germany united to underpin surplus and exaggerated (8)
I believe the answer is:
overdone
'exaggerated' is the definition.
(synonyms)
'germany united to underpin surplus' is the wordplay.
'germany' becomes 'd' (international vehicle registration code).
'united' becomes 'one' (as in a phrase like 'we are one').
'to underpin' says to put letters next to each other (in a down clue, some letters go under others).
'surplus' becomes 'over' (I've seen this before).
'd'+'one'='done'
'done' put after 'over' is 'OVERDONE'.
'and' acts as a link.
(Other definitions for overdone that I've seen before include "Hammed up" , "really a bit much!" , "Exaggerated; cooked too much" , "Cooked to excess" , "Cooked too much or carried too far" .)