Cannot add new roles at later stage, "Because the field already has data, some settings can no longer be changed."

This field update limitation can be really annoying. Usually you can ignore the message and update the field, but this is not the case. A simple workaround is to edit rolereference.module and comment line 57.

EDIT: this makes no sence.
devenderdagar, the status of your post was misleading: 'needs review' implies an attached patch.

Well, now it has... ;-)
If you do not check any of the roles in the field settings, they will ALL appear in the node edit/add form.
A newly created role will also appear.

OTOH, the same patch (but better) can be found here: #1280532: Allow any role to be referenced if none are explicitly selected.
marking this as a duplicate.

I do not consider this as duplicate. It's a different request. We are talking about the possibility to change the field configs after its creation.

EDIT: this makes no sence.
Then I do not understand what you mean. Maybe you need to run the following page after changing the settings: /admin/report/status/rebuild (For Rebuild permissions)
If so, the module should call variable_set('node_access_needs_rebuild', TRUE); after changing a role field.

I came across this issue. My remarks earlier are *** . I totally misunderstood the OP.
The proposed solution in #1 should do the trick. Below the explicit code.
(Setting this 1-line-patch to Needs Review, although there is no real patch-file.)

/**
 * Implements hook_field_settings_form().
 */
function rolereference_field_settings_form($field, $instance, $has_data) {
  $settings = $field['settings'];

  $form = array();
  $role_options = array_map('check_plain', user_roles());
  $form['referenceable_roles'] = array(
    '#type'          => 'checkboxes',
    '#title'         => t('Roles that can be referenced'),
    '#description'   => t('Select roles that may be referenced by this field. All roles will be available if none are checked.'),
    '#multiple'      => TRUE,
    '#default_value' => is_array($settings['referenceable_roles']) ? $settings['referenceable_roles'] : array(),
    '#options'       => $role_options,
-   '#disabled'      => $has_data,     // <== Remove this line.
  );
  return $form;
}

A proper patch.

#9 works for me

Tested this. Works for me