Mess up, having altered central feature of spooks’ function? (5)

I believe the answer is:

misdo

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'mess up' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for misdo that I've seen before include "Perform improperly" , "Perform wrongly" .)

I've seen this clue in The Times.

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