For an extract kit, you can bake about 2 cans of pumpkin in the oven until it starts to brown and/or caramelize a little and then add it to the steeping grains or even add it to the boil. I'm not sure what pumpkin flavoring you are referring to, but if it is just spices, then I would keep the spice additions as they are in the recipe. Adding the pumpkin will really only impact flavor a little and maybe the color but not add any real spice flavor.
Draft 3: Belgian Dubbel
Primary 1: German Hefe