Any Custom League commissioner can edit the roster of every team in their league. In order to allow league commissioners greater flexibility in dealing with dormant teams, the option to allow or disallow commissioner control has been removed.
As a commissioner, you can edit another team's roster by going to your Commissioner Tools page and choosing the "Edit Rosters" option. Once there, select the team you want to alter and the type of transaction from the pull-down menus. You're then presented with options that allow you to make themoves you want.
Since you can only control one team at a time, you must return to this page and follow the same procedure each time you want to control another team.