Technically, yes, but it may change the overall texture and flavor of the cookies from the extra molasses. Your pumpkin snickerdoodles will also come out darker in color. If you want to give it a try, I suggest using ½ cup each of white and light brown sugar. If they turn out well, you can test another batch using 3/4 cup of brown sugar and 1/4 cup of white sugar in the pumpkin snickerdoodle dough.