We have a class to create an administrator (CreateAdministrator.java) and a corresponding launcher (dspace create-administrator). This launcher also can be run in non-interactive mode by supplying data via options.
It has been asked several times how admins can batch-import users (using password authentication).
It would be trivial to duplicate the CreateAdministrator class to create any type of user (with group as an option) and then to modify the CreateAdministrator class to call this new class with the particular group=1.
Also, feel free to send here any other suggestions how to batch-create users from the command line.