This is some javascript and css code that allows you to have tabbed email and note replies in desk.com.

CaseThemeAddition.html

<script>
$(function() {
  var tid = $('#tabs .ui-state-active a').attr('href').replace('#tabs-tid_', '')
    , sel = '#email_reply_div_tid_' + tid
  
  setTimeout(function() {
    $(sel).prepend([
      '<div>',
      '  <ul class="reply-toggle">',
      '    <li class="active">',
      '      <a href=".a-ticket-reply">Email</a>',
      '    </li>',
      '    <li>',
      '      <a href=".a-note-reply">Note</a>',
      '    </li>',
      '  </ul>',
      '</div>'
    ].join(''));
    
    $(sel).append('<div class="a-note-reply hide">');
    $(sel + ' .a-yellow-button').hide();
  
    $.ajax($(sel + ' a.HK_add_note_link').attr('href'), {
      dataType: 'text',
      success: function(text) {
        var form = $('<div>' + text.match(/html\('(.*)'\)/)[1].replace(/\\n/g, '').replace(/\\/gi, '') + '</div>');
        form.find('.a-modal-actions .a-cancel').remove();
        form.find('.a-modal-actions .a-button.accept').prop('disabled', false).attr('onclick', function(idx, attr) {
          return 'resetNote("' + sel + '");' + attr;
        });
        $(sel + ' .a-note-reply').append(form.html());
        $(sel + ' .a-ticket-reply .a-user-icon').clone().insertBefore(sel + ' .a-note-reply .a-textarea');
      }
    });
  
    $(sel + ' .reply-toggle').on('click', 'li a', function() {
      $(this).closest('.reply-toggle').find('li').removeClass('active');
      $(this).closest('li').addClass('active');
      $(sel + ' .a-note-reply').addClass('hide');
      $(sel + ' .a-ticket-reply').addClass('hide');
      $(sel + ' ' + $(this).attr('href')).removeClass('hide').find('textarea').focus();
      return false;
    });
  
    $(sel + ' .reply-toggle a[href=".a-note-reply"]').click();
  }, 500);
  
  window.resetNote = function(sel) {
    setTimeout(function() {
      $(sel + ' .a-note-reply textarea').val('');
      $(sel + ' .a-note-reply .a-modal-actions .a-button.accept').prop('disabled', false);
    }, 500);
  };
});
</script>

<style>
  ul.reply-toggle { background: #D3C5E5; }
  ul.reply-toggle li { display: inline-block; cursor: pointer; }
  ul.reply-toggle li a { color: #2F2F2F; padding: 10px; display: block; }
  ul.reply-toggle li:hover { background: #AC96C9; }
  ul.reply-toggle li:hover a { color: #FFF; }
  ul.reply-toggle li.active { background: #EFE9F7; }
  ul.reply-toggle li.active a { color: #2F2F2F; }
  .a-note-reply { padding: 25px 15px 10px; }
  .a-note-reply .a-user-icon { float: left; }
  .a-note-reply .a-modal-actions, .a-note-reply .a-textarea, .a-note-reply .agent_light_text { margin: 0 12px 0 65px; display: block; }
  .a-note-reply .a-modal-actions:after { display: block; content: ''; clear: both; }
  .a-note-reply .a-textarea, .a-note-reply textarea { background: lightyellow; }
</style>