Changing partners, I come out! (9)
I believe the answer is:
transpire
'come out' is the definition.
(I've seen this before)
'changing partners i' is the wordplay.
'changing' is an anagram indicator.
'partners'+'i'='partnersi'
'partnersi' anagrammed gives 'TRANSPIRE'.
(Other definitions for transpire that I've seen before include "Lose water vapour" , "Terrapins (anag)" , "revealed" , "Turn out" , "give off water vapour" .)