It is possible to modify a shift already scheduled, even if the shift is already published. It will then be possible to send a shift change notification to the employees.
Identify the quarter you want to modify, then right click and modify:
2. Makes the necessary changes to the shift, such as changing the employee, start or end times, adding a break, etc.
3. By default, the system will notify the employee about the change. You can choose to uncheck it if you don't want to notify the employee.