Edit

As of WP 4.3 this won’t work anymore. WP have completely removed the javascript for the old distraction-free mode.

To use this in 4.3 versions, get a copy of javascript file from WP 4.2 release and enqueue it before using code below.

---

You can:

1. use 'wp_editor_settings' filter to set the '_content_editor_dfw' option to false.

2. use 'mce_buttons' and 'teeny_mce_buttons' filters to:

   • remove new distraction-free button, that has id: 'dfw'
   • add the old distraction-free button that has the id: 'wp_fullscreen'

3. use 'tiny_mce_plugins' and 'teeny_mce_plugins' filters to add the old plugin script, that luckily wasn’t removed, it is named 'wpfullscreen'

For #1 and #2 you can check that the editor your editing is the one with id 'content'.

All steps above as a plugin (available as a Gist here):

<?php namespace GM\FSDFM;
/**
 * Plugin Name: Fullscreen Distraction-Free Mode (pre v4.1)
 * Plugin URI: https://gist.github.com/Giuseppe-Mazzapica/c081ce03a68b00d983d5
 * License: MIT
 */

if (!is_admin()) return;

function should($editor_id = 'content') {
  return (version_compare($GLOBALS['wp_version'], '4.1') >= 0)
    && in_array($GLOBALS['pagenow'], array('post.php','post-new.php'))
    && $editor_id === 'content';
}

function buttons($buttons, $editor_id) {
  return should($editor_id)
    ? array_diff(array_merge((array) $buttons, array('wp_fullscreen')), array('dfw'))
    : $buttons;
}

function plugins($plugins) {
  return should()
    ? array_diff(array_merge((array) $plugins, array('wpfullscreen')), array('fullscreen'))
    : $plugins;
}

function settings($settings, $editor_id) {
  if (should($editor_id)) {
    $settings['_content_editor_dfw'] = false;
  }
  return $settings;
}

add_filter('wp_editor_settings', __NAMESPACE__.'\\settings', 30, 2);
add_filter('mce_buttons', __NAMESPACE__.'\\buttons', 30, 2);
add_filter('teeny_mce_buttons', __NAMESPACE__.'\\buttons', 30, 2);
add_filter('teeny_mce_plugins', __NAMESPACE__.'\\plugins');
add_filter('tiny_mce_plugins', __NAMESPACE__.'\\plugins');