Also, this may be a long way (and remove your student data though) but in (2.6), but you can go to your course, then
-Users - Enrollment Methods- Manual Enrollments
Find the cohort sync, and click on the X to delete it.
Then Enrol the chohort manually, so all the users appear with action icons next to their names and you'll be able to suspend the individual.
Cohort Sync is great if the people in the group will be changing often. Otherwise, I like to stick with manually enrolling a cohort.