[Solved] ThemeKey Random Theme For Session

Here's how you can do it:

1) Create a block for your theme switcher:

function my_module_block_info()
{
  $blocks['theme_switcher'] = array
  (
    'info' => t('Theme switcher'),
    'cache' => DRUPAL_CACHE_GLOBAL,
  );
  return $blocks;
}

function my_module_block_view($delta = '')
{
  if($delta == 'theme_switcher')
  {
    $block = array
    (
      'subject' => t('Language Switcher'),
      'content' => array
      (
        'form' => drupal_get_form('language_switcher_form'),
      ),
    );

    return $block;
  }
}

Then you declare the form to switch language:

function language_switcher_form($form, &$form_state)
{
  $form['submit'] = array
  (
    '#type' => 'submit',
    '#value' => t('Change theme'),
  );
  return $form;
}

function language_switcher_form_submit($form, &$form_state)
{
  $themes = array('default_theme_name', 'theme_1', 'theme_2');
  $random = rand(0, count($themes) - 1);
  $_SESSION['custom_theme'] = $themes[$random];
}

Finally, you set the theme to be used in hook_custom_theme:

function my_module_custom_theme()
{
  if(!isset($_SESSION['custom_theme']))
  {
    return 'default_theme_name';
  }

  return $_SESSION['custom_theme'];
}

You can now use your block that has been created, that will add a button with which the user can change the theme. A random theme will be applied and will be used until the button is pressed again.

Note that default_theme_name, theme_1, and theme_2 must all be enabled for this to work.