Acknowledge set of rules involving New Church (7)
I believe the answer is:
concede
'acknowledge' is the definition.
(conceding is a kind of acknowledging)
'set of rules involving new church' is the wordplay.
'set of rules' becomes 'code' (I've seen this before).
'involving' means one lot of letters goes inside another.
'new' becomes 'n'.
'church' becomes 'ce' (abbreviation for Church of England).
'n'+'ce'='nce'
'code' enclosing 'nce' is 'CONCEDE'.
(Other definitions for concede that I've seen before include "Surrender, yield" , "Make admission" , "Yield; grant" , "Admit something is true" , "Admit (defeat in match)" .)