Yes you can edit your live site by using the URL yourdomain.com/#edit and then logging in using your login credentials.  I strongly recommend you use a strong password with your unique ID.  Also, if you have employees working on your site we also recommend adding them as a Sub-account user and not handing out your main login credentials.   You can contact support to add sub-account user access.  It's a free option for your website.

Also, with the new builder you can publish a single page!  When you are on the Preview Tab and click the "publish page" button you will get a pop up that gives you the choice to publish the page you are working on or the entire site.