You can customize the button, sign in to addthis.com and then visit this url: http://addthis.com/help/custom-buttons
I don't have a way yet for you t customize the AddThisButton in the blog so you might disable that one and just use the main one in the page. These customization options are new beta features of addthis.com.
I do not believe you can remove the footer. If you need to do that then you'll have to come up with your own bookmarking technique instead of using the free addthis.com service.
Hope it helps,