Alternate way under different conditions (9)
I believe the answer is:
otherwise
'under different conditions' is the definition.
(I've seen this before)
'alternate way' is the wordplay.
'alternate' becomes 'other' (I've seen this in another clue).
'way' becomes 'wise' (wise is a kind of way).
'other'+'wise'='OTHERWISE'
(Other definitions for otherwise that I've seen before include "Apart from that" , "Differently - or else!" , "In other respects or ways" , "in different circumstances" , "White rose (anag.)" .)