Blogger allows you to download your entire blog.  Go to "settings" "basic" and you will see the choices - to import blog, to export blog, and even to 'delete blog'.

You'll want to "export" and it will save to your desktop.  That way, if you make a mistake while tweaking your blog or need to delete it and start over, you can upload all your posts and comments (provided you are using the blogger commenting system).  I'm not sure how this works when using disqus because I haven't tried it yet with a blog that has disqus installed.
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