How to override function system_send_email_action_validate The following is in the core system.module

/**
 * Validate system_send_email_action form submissions.
 */
function system_send_email_action_validate($form, $form_state) {
  $form_values = $form_state['values'];
  // Validate the configuration form.
  if (!valid_email_address($form_values['recipient']) &amp;&amp; strpos($form_values['recipient'], ':mail') === FALSE) {
    // We want the literal %author placeholder to be emphasized in the error message.
    form_set_error('recipient', t('Enter a valid email address or use a token e-mail address such as %author.', array('%author' =&gt; '[node:author:mail]')));
  }
}


This is stopping VBO send email from sending email to a CCK email field.
How can I override this function? I want to change it to the following...

/**
 * Validate system_send_email_action form submissions.
 */
function system_send_email_action_validate($form, $form_state) {
  $form_values = $form_state['values'];
$has_tokens = count(token_scan($form_values['recipient'])) &gt; 0 ? TRUE : FALSE;
  // Validate the configuration form.
  if (!valid_email_address($form_values['recipient']) &amp;&amp; !$has_tokens) {
    // We want the literal %author placeholder to be emphasized in the error message.
    form_set_error('recipient', t('Enter a valid email address or use a token e-mail address such as %author.', array('%author' =&gt; '[node:author:mail]')));
  }
}


But without hacking core. Is there a way to do this in my custom module? Im having a bit of trouble understanding how overriding a module function works, in theme functions, I can just replace the function in mt template.php using the name of my theme, however MYMODULE_system_send_email_action doesnt work.
You can use "hook_preprocess_HOOK"