This question comes up on a fairly regular basis.

Yes, pasta is dried. But it's not cooked, which is the issue. Cooking the pasta at home and then dehydrating it makes all the difference in the world.

In your case, using the instant mac and cheese should work, because that uses pre-cooked pasta. Test it at home first.

In fact, testing any recipe at home is a good idea. To add realism, cook it on your backpacking stove outside, preferably when it's windy and raining. (I am being totally serious.)