Party supplier transformed terrace (7)
I believe the answer is:
caterer
'party supplier' is the definition.
(I've seen this in another clue)
'transformed terrace' is the wordplay.
'transformed' indicates anagramming the letters.
'terrace' with letters rearranged gives 'CATERER'.
(Other definitions for caterer that I've seen before include "Someone providing food and service" , "Refreshment supplier" , "One supplying cheer" , "Someone needed for party" , "Provider of refreshments" .)