You can show preheader and prefooter from « Content » tab, when no block is selected in the newsletter.
Select the preheader or prefooter block to edit.
Click on the « Style » tab to customize the mirror or unsubscribe link text.
If you want a specific design for this links, do not show preheader and prefooter, and use another block. Then you can add the mirror link or the unsubscribe link by yourself.
Here is the tag for the mirror link: %WEBCOPY%, in the Url field.
Here is the tag for the unsubscribe link: %UNSUBSCRIBELINK% . This one is mandatory.