The Project can be made private, and the administrator(s) will be able to determine which players will have access to the challenges (activities and actionables).
For every new group/cohort, and assuming that groups/cohorts will not be attempting the game in parallel, the list of invited players can be edited / added to / removed from the Project. This will enable the administrator to limit access to specific players from the same groups/cohorts, and making the Project inaccessible by those who are from another group/cohort.
Additionally, if there are multiple groups/cohorts being invited, the challenges (activities and actionables) for each cohort can be segmented as a Topic, and the feature to privatise content is also available on a Topic level. Hence, you can limit access to content for players specific to their groups/cohorts.