Stand-in's responsibility to keep record (6)
I believe the answer is:
deputy
'stand-in's' is the definition.
(I've seen this before)
'responsibility to keep record' is the wordplay.
'responsibility' becomes 'duty' (synonyms).
'to keep' means one lot of letters goes inside another.
'record' becomes 'EP' (abbreviation for extended play record).
'duty' going around 'ep' is 'DEPUTY'.
(Other definitions for deputy that I've seen before include "mine safety official" , "Person appointed to act as substitute" , "Second in command" , "US sheriff's assistant" , "Not the principal" .)