Try cab - let change be the slogan! (6,3)
I believe the answer is:
battle cry
'the slogan' is the definition.
(I've seen this before)
'try cab let change' is the wordplay.
'change' is an anagram indicator.
'try'+'cab'+'let'='trycablet'
'trycablet' anagrammed gives 'BATTLE-CRY'.
'be' acts as a link.
(Other definitions for battle cry that I've seen before include "Martial slogan" , "Geronimo, for example" , "Slogan (for those going into a fight?)" , "jingoistic shout" .)