Change order of custom profile fields on Drupal register page
You need to use a hook_form_alter function in Drupal to accomplish this. In doing so, you can modify the weight of the items to appear below the existing form items.

function yourmod_form_alter(&amp;$form, &amp;$form_state, $formID) {
  if (($formID == 'user_register_form')) {
    $form['civicrm-profile-register']['#weight'] = somevalue;
  }
}