Starting with SPS 10 it is now possible to specify ORDER BY for STRING_AGG. Example:
SELECT
X,
STRING_AGG(Y, ',' ORDER BY Y) Y
FROM
( SELECT '1000' X, 'C' Y FROM DUMMY UNION ALL
SELECT '1000' X, 'A' Y FROM DUMMY UNION ALL
SELECT '1000' X, 'B' Y FROM DUMMY UNION ALL
SELECT '2000' X, 'C' Y FROM DUMMY
)
GROUP BY
X
ORDER BY
X
