Like @tamdamson said, I also think you can't get deep enough to change that.
If you pay attention to the code you posted, will notice that it isn't HTML+CSS. It is a XSLT stylesheet, ie, a XML document.
The advantage of using that kind of document is: you can declare repetition rules, and wrap snippets (templates) into other files.
Can you find even the blog post code in the code you sent? No. You find a call to a widget (a file with rules for processing blog posts). You can change it going into Design mode and editing the blog posts widget.
Comments are another widget called inside blog posts. But you don't have access to this one AFAIK. Thus you can't change the nofollow to follow.