As noted in the post, this recipe can be adapted to your liking. Shapes like penne are more traditional but campanelle, which means "bellflowers" in Italian, has fluted, petal-like edges which crisp up nicely in the oven and look pretty. Any shape, however, will work just fine. You can use Pecorino or Grana Padano in place of the Parmigiano Reggiano. For the second cheese, I love to use mozzarella or Fontina, but something like Gruyère or Comte would work well, too. And as for fillings, add what you like. I love the simplicity of raw greens and maybe a little browned sausage, but use what you have on hand.