I implemented --admin-user|-A when creating a new repo file. I did not implement supplying the password on the command line. That can be changed easily enough in the ui or via fossil user password USERNAME PASSWORD. Setting the default user could not be altered before history was already created for that user.

As for adding a user in addition to the default admin user, you can do that after the repo is created via the ui or fossil user new ?USERNAME? ?CONTACT-INFO? ?PASSWORD?. Therefore, I am going to close this ticket.