One with no illusions is alert to change (7)
I believe the answer is:
realist
'one with no illusions' is the definition.
(I've seen this before)
'is alert to change' is the wordplay.
'to change' indicates anagramming the letters.
'is'+'alert'='isalert'
'isalert' with letters rearranged gives 'REALIST'.
(Other definitions for realist that I've seen before include "who may look for practical solution" , "Person who sees things without illusions" , "Practical type" , "Plato, for example" , "Practical sort" .)