At times we need to change the message that is displayed after a node is saved.Follwing code helps to customize using form_alter.

function mymodule_form_alter(&$form, &$form_state, $form_id) 
{
    if($form['form_id']['#value'] =='formvalue')
    {   
          if($form['buttons']['submit']['#submit']){
            $form['buttons']['submit']['#submit'][] = 'mymodule_submit_function';
          }
    }
}

function mymodule_submit_function($form, &$form_state){

    global $_SESSION;
    $insert = empty($form_state['values']['nid']);
    if($insert){
        //Write your custom message text here
        if($form['nid']['#post']['form_id'] == 'formvalue'){
            $keys = array_keys($_SESSION['messages']['status']);
            $last_key = end($keys);
            $message = 'My custom messge after node save';
            $_SESSION['messages']['status'][$last_key] = $message;
        }
    }
}