Of course, you can use a long sharp knife to cut the cereal carefully, however, don't run it through the dough, but instead place it gently down onto the dough to cut your lines. What works even better (and easier) in my opinion, is using a pizza cutter to carefully run it alongside the edges you'd like to cut. Do this gently and slowly with only a little bit of pressure applied, as you don't want to cut all the way through the baking parchment.