title: Change service config parameters at runtime
body: <p>I'm using mailgun to send mails thought Laravel 5.2. It configured on config/services.php like that:</p>
  
  <pre><code>    'mailgun' =&gt; [
          'domain' =&gt; env('mailgun_domain','mydomain.com'),
          'secret' =&gt; env('mailgin_secret','my-secret-key-132152345423')
      ],
  </code></pre>
  
  <p>But, I need change that settings in run time, before call Mail::send, to use the correct service parameters. It must be changed many times during runtime.</p>
  
  <p>I <strong>cannot configure it by .env file</strong>, because all data will be get from database, where the user setups the domain and secret.</p>