Thought I would share this link to my version; since I will have to publish it anyway in a couple of weeks when it wins the Best of Show at the HBT competition
https://www.homebrewtalk.com/f76/lady-rumpkin-pumpkin-rum-ale-214177/
I am going to do another batch next month and let it age until fall, much like you plan on doing. What I found when I sent out the bottle to the finals is that the alcohol rum edge that it had last fall really receded into the background, in a word, Delicious! I think 4-6 months in the cellar did wonders for it!
Edit: In my excitement over seeing "pumpkin ale" I missed your question entirely, which of course has been answered. Brown sugar aside, I think the excellent reviewed Thunderstruck uses a pumpkin spice "tea" in secondary (as I did with the Rumpkin) which perhaps you would consider instead of adding the spice at flameout. It all depends on the flavor profile and intensity you are shooting for, of course.