The file is now skin/common_files/main/history_order.tpl. Pretty much the same change. Find this:
Code:
<input type="text" name="tracking" value="{$order.tracking|escape}" />
Change to this:
Code:
<input type="text" name="tracking" value="{if $order.tracking eq ''}12345678{else}{$order.tracking|escape}{/if}" />