An actual "Update", it may not be possible, but have you consider and will something like this work for you? This is simulating updates within the query without actual UPDATE statements:
CREATE OR REPLACE TABLE table1 AS
WITH CTE1 AS (
-- Your initial query for CTE1
),
CTE2 AS (
SELECT
CASE WHEN condition THEN updated_value ELSE original_value END AS column_name,
...
FROM CTE1
),
CTE3 AS (
SELECT *
FROM CTE2
)
SELECT *
FROM CTE3;
Feel free to clarify if there's a misunderstanding about the requirement. Meanwhile, hope it helps.