I was under the same impression as stampsyne. You're not supposed to cover up any of your lookup information, I believe that includes all the text and and shields, sorry
Having said that, people still continue to cover their shields, according the the csshelp petpage the css for cover the shield is:
Code:
<style>i.shield{background:url(http://www.boomspeed.com/spacefreak/shieldz/redshield.gif);
height:221;width:100;position:absolute;top:360;left:596}</style><i class=shield> </i>
You'll just have to alter the URL to your own one
If you're only looking to change say, the month text or something then you'll need to have a graphic that has what you want on it and then just alter the position values in the code so it ends up in the correct location.