Tight-lipped about a temperature change (6)
I believe the answer is:
mutate
'change' is the definition.
(mutating is a kind of changing)
'tight-lipped about a temperature' is the wordplay.
'tight lipped' becomes 'mute' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'temperature' becomes 't' (abbreviation).
'a'+'t'='at'
'mute' going around 'at' is 'MUTATE'.
Can you help me to learn more?
(Other definitions for mutate that I've seen before include "Change in genetic way, perhaps from radiation" , "(In genetics) change" , "Undergo change to another form" , "Change into something else" , "Undergo cellular change" .)