It seems that Wikimetrics can't alter cohort, making it inconvenient for real use. In Thai Wikipedia, for example, we have a number of special volunteers that will contribute to the project, and we want to track their changes. The number of these special volunteers are not constant. Therefore, every time a new volunteer appears we have to create a new cohort. This is very ineffective. Making Wikimetrics can edit list of users would solve the problem.