Meddle with untried arrangement (7)
I believe the answer is:
intrude
'meddle' is the definition.
(I've seen this before)
'untried arrangement' is the wordplay.
'arrangement' indicates an anagram.
'untried' is an anagram of 'INTRUDE'.
'with' acts as a link.
(Other definitions for intrude that I've seen before include "Push in where not wanted" , "Butt in, interfere" , "Join in without being invited or wanted" , "Encroach on others' privacy" , "Break in" .)