Changing layout of panel on the fly

gistfile1.txt

/**
 * Implements hook_panels_pre_render().
 */
function custom_panels_pre_render($display, $renderer) {
  // To switch a panel's layout on the fly, you need to not only set
  // the display's layout, but also swap out the layout plugin in the
  // renderer object.
  ctools_include('plugins', 'panels');
  if ($plugin = panels_get_layout($layout)) {
    $display->layout = $layout;
    $renderer->plugins['layout'] = $plugin;
  }
}