Said they'll jemmy it open to get a reward (5)
I believe the answer is:
prize
'a reward' is the definition.
(I know that reward is a more specific form of recognise)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for prize that I've seen before include "Reward for having won a contest" , "See 16" , "Award; value highly" , "Trophy" , "something of great value?" .)