elife_newsletter_marketing_messages.module

<?php
function elife_newsletter_marketing_messages_menu() {

  $items['newsletters/marketing-message'] = [
    'page callback' => 'elife_newsletter_marketing_messages_render',
    'access callback' => TRUE,
  ];

  $items['civicrm/mailing/elife-marketing-messages'] = [
    'title' => 'Marketing messages for newsletters',
    'page callback' => 'drupal_get_form',
    'page arguments' => ['elife_newsletter_marketing_messages_form'],
    'access arguments' => ['Edit marketing messages in elife newsletters'],
  ];

  return $items;
}

function elife_newsletter_marketing_messages_permission() {
  return array(
    'Edit marketing messages in elife newsletters' => array(
      'title' => t('Edit marketing messages in elife newsletters'),
    ),
  );
}


function elife_newsletter_marketing_messages_render($type) {
  drupal_json_output(['html' => variable_get("elife_newsletter_marketing_messages_{$type}_message")]);
}

function elife_newsletter_marketing_messages_form($form) {

  $helpText = 'Only include plain text with html &lt;a&gt; tags, e.g. \'Find out more about &lt;a href="https://elifesciences.org/about?{track}""&gt;eLife sciences&lt;/a&gt;\'.
               To add the default tracking params, add a {track} token as a query param. Remember to add a \'?\' or \'&\' as appropriate before the token.';

  $form['elife_newsletter_marketing_messages_vor_message'] = [
      '#title' => 'VOR marketing message',
      '#type' => 'textarea',
      '#description' => $helpText,
      '#default_value' => variable_get('elife_newsletter_marketing_messages_vor_message', 'Find out more about <a href="https://elifesciences.org/about?{track}"">eLife sciences</a>')
    ];
  $form['elife_newsletter_marketing_messages_poa_message'] = [
      '#title' => 'POA marketing message',
      '#type' => 'textarea',
      '#description' => $helpText,
      '#default_value' => variable_get('elife_newsletter_marketing_messages_poa_message', 'Find out more about <a href="https://elifesciences.org/about?{track}"">eLife sciences</a>')

  ];

  return system_settings_form($form);

}