Add hook to provide notice of changes to DJs or scheduled times

I need to write some code to track changes to the schedule for the station's security list. When people are added or removed from shows, their show is scheduled or unscheduled, or the show moves time slots, I need to know so their access to the station can be modified. I started trying to do it as a bunch of nodeapi and form_alter code but it's complex enough that it'd be better to have the schedule just call a hook to provide notices.