Thank you. You’d need the CSS upgrade and a knowledge of CSS. You can test out whether or not you can make the changes in the free Preview and then, once you’ve got it working, buy the upgrade. Don’t buy it if you don’t know CSS. You’re essentially on your own with it.
Instead of messing with CSS, you can easily put a copyright notice in a text widget. You can also add such a notice at the end of each post — but not automatically, you’d need to do that manually for each post.