#standardSQL
SELECT REGEXP_REPLACE(
"Name,Door_No,Street_Name,Area_Name,State_Name,12345",
r"([^,]*,)([^,]*,)([^,]*,)([^,]*,)([^,]*)(,[^,]*)",
r"\1\2\3\4California\6"
) AS example
returns
Row example
1 Name,Door_No,Street_Name,Area_Name,California,12345