Humus an excellent material to add to your pile, but if your pile is already at capacity, the humus will simply become part of the pile. It will not generate heat. And the more you add, the less likely it is that heat will be generated, because there’s less air in the pile. My advice: Break up your pile now, add some more browns and greens, and give your pile a vigorous mixing. Let it heat up a little more. Then, when it has cooled down, add some of the humus you purchased.