Other half to make changes? Say nothing! (5,3)
I believe the answer is:
'other half' is the definition.
(I've seen this before)
'make changes? say nothing' is the wordplay.
'make changes?' becomes 'alter' (I've seen this in another clue).
'say' becomes 'eg' (both can mean 'for example').
'nothing' becomes 'o' (looks like zero - 0).
'to' is the link.
(Other definitions for alter ego that I've seen before include "Hidden or second self - in Latin" , "Similar character" , "bosom buddy" , "A person's secondary personality" , "Go, relate to other self" .)