Like most candy recipes, there isn't room for ingredient substitution. I always recommend following the recipe as written. I find these truffles get even better-- and the pumpkin flavor becomes more prominent-- after a day or two in the refrigerator.
Pumpkin Lasagna - a delicious layered dessert with a Pumpkin Oreo crust, cream cheese layer, pumpkin pudding layer, and topped with cream and white chocolate curls. I'm not sure how I feel about all of the manufacturer ingredients, but I'm willing to try!