I don't think that we can actually make this replacement. The parenthesis are complicated here, but here's what it seems to be saying (from innermost parenthesis to outermost):

First, see if admin in checkout mode, ```or``` checkoutperson. 
Then, see if that result ```and @user.id==nil```
Then, see if admin in admin mode, ```or``` that whole reduction described above.
Then, if either side of that is true, check ```if current_user and``` everything up to here.

In short, the login input form can only be edited by admins in checkout mode and checkoutpersons when their user id is nil. Otherwise, it's only accessible to admins in admin mode. That being said, I'm confused as to how this would ever happen -- how could someone be logged in with a session (```current_user != nil```) yet not be assigned a user id?

Finally, looking at the ApplicationSetupController, I don't think that this view will ever even render in the first place -- we changed the ```new_admin_user``` method to redirect to the ```new_user_path```. If this is truly the case, we should probably also remove the create_admin_user method from ApplicationSetupController.

Sorry for the verbosity of this comment, just let me know what you think would work the best.