Cockney in to cut deal, one predicting change (9)
I believe the answer is:
barometer
'one predicting change' is the definition.
'cockney in to cut deal' is the wordplay.
'cockney in' becomes 'ome' ('home' - 'he's in' can mean 'he's home' - said with the 'H' dropped - a cockney accent.).
'to cut' is an insertion indicator.
'deal' becomes 'barter'.
'ome' inserted inside 'barter' is 'BAROMETER'.
(Other definitions for barometer that I've seen before include "Weatherglass" , "It measures air pressure" , "Weather forecaster" , "Pressure gauge" , "Instrument that measures atmospheric pressure" .)