State’s old name-alternative happens to be “South Africa” (6)
I believe the answer is:
orissa
'state's old name' is the definition.
(former name of the Indian state Odisha)
'alternative happens to be south africa' is the wordplay.
'alternative' becomes 'or'.
'happens' becomes 'is' (to be can mean to happen).
'to be south africa' becomes 'sa' (abbreviation).
'or'+'is'+'sa'='ORISSA'
(Other definitions for orissa that I've seen before include "This is on India's eastern coast" , "Indian state" , "state of India?" .)