You wouldn’t have to create new categories, articles or modules. That’s all content stuff, so don’t worry about that.
Positions on the other hand …
Best-case scenario is you install a new template, meaning you’d have to do some modifying of the index.php and a few other configurations to make sure you have the same module positions and so on. It might be a little tricky but generally that’s the idea behind a CMS like Wordpress or Joomla … is that you have the ability to swap out templates without necessarily affecting your site’s content.
Otherwise … there’s this thing called CSS. You might consider learning some of it.