Performed first part of play cold? That's edifying (8)
I believe the answer is:
didactic
'edifying' is the definition.
(I've seen this before)
'performed first part of play cold?' is the wordplay.
'performed' becomes 'did' ('do' can be a synonym of 'perform').
'first part of play' becomes 'Act I' (Act 1 in a play).
'cold?' becomes 'c' (eg on taps).
'did'+'acti'+'c'='DIDACTIC'
'that's' acts as a link.
(Other definitions for didactic that I've seen before include "giving instruction" , "'Instructive, perhaps excessively so (8)'" , "Having the manner of one lecturing pupils" , "Teaching morally" , "Imparting a lesson" .)