insert a div tag before wpwrap div

ive been playing around with the wp-admin css stylesheet.

lets say, i wanted to create a new <DIV> on top of the

<div id=”wpwrap”> in adminheader.php

and a closing tag below the </body> on adminfooter.php

should i just go create a new div manually? or use a plugin to insert those html <div> tags.

thanks.