UL 489 (for low-voltage molded-case and insulated case circuit breakers) is silent regarding any form of de-rating for ambient environments greater than 40C.

UL 1066 (for low-voltage power circuit breakers) is also silent on the topic, however UL 1558 (low-voltage switchgear) does allow for de-rating in accordance with ANSI/IEEE C37.20.1, and may be used when applicable.