Yes. You can easily increase the amounts of the ingredients and turn this into a big batch cocktail. If making ahead of time, I recommend muddling the blackberries, honey and lemon juice and straining it into a pitcher. Stop at this point and wait to add the gin when you're ready to serve. Adding the ice and the sparkling water into the pitcher is up to you, but it will dilute the cocktail. I recommend leaving them out and having a bucket of ice and bottles of sparkling water out so guests can add however much they want.