Good thinking and exploration by Sebastian Eberlein. I'm a firm believer that you're doing yourself a favor if you blog in Markdown, because it gives you clean HTML output that isn't littered with classes very likely won't last forever.
Instead, why not use some clever CSS selectors (using stuff like adjacent sibling combinators) to get the spacing and styling you want without changing the markup. CSS is a lot easier to change than HTML. HTML within content, that is. HTML as part of templates is just as easy to change.