Let it carb up, see if you like it. If then,you don't you can take a tablespoon of pumpkin pie spice and put it into a mason jar of cheap vodka, let it sit a week or two, shaking it every day. The vodka will take on the taste and aroma of the spice. run the mixture through a coffee filter when you want to use it, then you can add however much you want to your carbed keg, a teaspoon at a time. The flavor addition should be immediate and you can dial it in where you want it.