The only time providers can change their time frame without removing bookings is if they are adding dates to the schedule. In all other cases, providers cannot remove or switch schedule dates on a time frame that has bookings.
If you're in a situation where you need to change schedule dates - but you have bookings on your time frame already - the most efficient option is to remove the students, make your schedule changes, and then rebook the students, from the roster page. Follow the steps below:
1) Remove the students from the entire semester/camp roster
2) Then, make the time frame changes:
Schedules> Semesters/Camps> click one of your schedule time containers> Semester/Camp Actions> Edit Semester/Camp
3) Once you finish the changes to the time container you'll now have to rebook each student in the roster:
Upcoming or the Semester/Camp Summary> Canceled tab (to the top left)> [...] (on each student)> Rebook Student