Configure specific day(s) to flag or notify users that additional charges may apply

We have to continually reach out to folks that have booked events for the school year, but included breaks and holidays. It would be great to flag or prompt a notice stating that custodial charges may apply because hours are different. In most cases, folks do not intend to book the particular day or week, but don't stop to think about it. This would help cut down on the work we perform in following up and confirming things are or are not really happening.