If a manual change is made in a schedule (i.e. enroll one student in a course) and you save the snapshot after making the manual change, this change will remain after restoring the snapshot.

If the manual change is made and then you create the snapshot, that snapshot will have the manual change included.
If the manual change is made after saving the snapshot, the manual change will not appear after restoring the snapshot. You can view the help topic Schedule Snapshots for more information.