Astute change of topic, being out to corner one! (7)
I believe the answer is:
politic
'astute' is the definition.
(thesaurus)
'change of topic being out to corner one' is the wordplay.
'change of' is an anagram indicator (the letter order is changed).
'being out' means one lot of letters goes inside another.
'to corner one' becomes 'li' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'topic' anagrammed gives 'potic'.
'potic' going around 'li' is 'POLITIC'.
Can you help me to learn more?
(Other definitions for politic that I've seen before include "Sensible, judicious" , "Expedient" , "Prudent, discreet" , "Prudent, sagacious" , "Wise, cautious" .)