Can I cook a food differently than the instruction?
You can cook your food any way that you like, or is practical.  There are two issue to consider.  First, is the packaged product already fully cooked (and thus only needs reheating) or does it need to be fully cooked?  Your cooking or reheating procedure should be appropriate for this first distinction.  Secondly, if you use a cooking procedure different from the one specified on the package, your results might differ from the picture or the product's instructions.  However, as long as you cook or re-heat appropriately, the product will be safe to eat.