I'm not familiar with the kit but if it is a vodka potion that you are adding prior to bottling then once you rack all of your beer to your bottling bucket you should just add a little bit of the potion, swirl it a bit, take a taste and then decide if you want to add more. Get the correct flavor you want before actually bottling and capping then you should be good to go. Do note that the spices will fade a little bit over time. Cheers!
"24 hours in a day, 24 beers in a case. Coincidence?"
-- Stephen Wright