I'm thinking of making a Blackberry smoked porter,from a brewers best kit, letting it age and condition with honey for about 4 months.
will this work to let the blackberry mellow out and not be so overpowering?
You can add it, but I suspect you will probably not notice it. Not much blackberry, and the sugar will just be fermented out. Make sure there are no preservatives in there that will kill the yeast.