Consent to change gear with energy (5)
I believe the answer is:
agree
'consent to' is the definition.
(agreeing is a kind of consenting to)
'change gear with energy' is the wordplay.
'change' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'gear' is an anagram of 'agre'.
'agre'+'e'='AGREE'
(Other definitions for agree that I've seen before include "concede" , "Say yes to a suggestion" , "Concur - correspond" , "Have the same opinion" , "Allow" .)