Competitor making no changes to accommodate temperature and energy (10)
I believe the answer is:
contestant
'competitor' is the definition.
(someone competing in a game)
'making no changes to accommodate temperature and energy' is the wordplay.
'making no changes' becomes 'constant' (something constant is unchanging).
'to accommodate' is an insertion indicator.
'temperature' becomes 't' (abbreviation).
'and' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
't'+'e'='te'
'constant' enclosing 'te' is 'CONTESTANT'.
(Other definitions for contestant that I've seen before include "One in quiz" , "One entering a competition" , "One of those competing" , "Competitor" , "Person vying with others" .)