After the timetable has been generated, until a register associated with any event created from the blocking process has been marked, it is still possible to modify blocks and periods or course group allocations in Block Matrix and regenerate the timetable.
Care should be taken as regeneration will remove all existing events for courses that are scheduled using the blocking process, which will include any events that have been manually added through ebs: shape and may require the re-issuing of all staff, room, and learner timetables.
Once any register for a course included in the block matrix process has been marked, the timetable is automatically locked and cannot be regenerated. This is indicated by the status of the Learners Locked option in the Session group of the ribbon.
It is also possible for an administrator to lock down the current allocations of learners to groups manually using this option.