Hiding field groups during registration
you can do this with using hook_form_alter

You can do something like this:

function YOUR_MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    if($form_id == 'your_form_name') {
        //do what ever you want
        //$form is an array of form elements, to delete some of them you can just do:
        unset($form['your-element-name']);
        //or and I think it is more "drupal way" to do things you can hide an element using hide function, e.g.:
        hide($form['account']);
    }
}