Meddle (with) (6)
I believe the answer is:
tamper
'meddle with' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tamper that I've seen before include "Interfere harmfully" , "Meddle or interfere with" , "Fiddle" , "Machine for compacting earth; interfere (with)" , "Interfere (with something) without permission" .)