There are ways to bulk create cohorts, but apparently not to maintain them (eg edit or remove)
e.g. I created over a 100 cohorts using CSV file, which should now contain different students.
I can't find a way to remove students from a cohort using CSV.
I also can't find a way to remove cohorts using CSV .
I suggest adding an extra field, something like:
jackbrown,Pass5678,Jack,Brown,firstname.lastname@example.org,London Contingent,Oxford Contingent