How to change the user registration form markup I want to change the markup on the user registration form that reads 


  Spaces are allowed; punctuation is not allowed except for periods,
  hyphens, apostrophes, and underscores.


and


  A valid e-mail address. All e-mails from the system will be sent to
  this address. The e-mail address is not made public and will only be
  used if you wish to receive a new password or wish to receive certain
  news or notifications by e-mail.


to something more friendly.  

I don't think String Overrides works with the registration form so I guess I need a custom module - hook_form_alter perhaps?
You can do that by implementing hook_form_alter() in your custom module:

For ex:

function MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if($form_id == 'user_register_form') {
    //dpm($form);
    $form['account']['name']['#description'] = t('Your Custom Text');
  }
}


To add Markup you should look into theme_form_element.