by Carlo Ditan.
I just managed to backup a section via CLI by section ID (did some minor tinkering on my local Moodle instance). The prerequisite is that the section and course ID pair should be present in the course_sections table.
$ php admin/cli/backup.php --courseid=2 --sectionid=17
Is there a way to fetch the course sections that have been modified recently (for example, all the course sections that have been modified today)?