You can add vanilla, and porters are great beers to do this with. I however, would not want to add vanilla to a smoked porter. The thing with adding stuff like extract is that you want to try a small sample size and use a dropper to add the extract into that sample and taste until you get the right flavor you are looking for. Then you can scale up to see how much you should add to the full batch and bottle. Also make sure you use a high quality vanilla extract and not imitation vanilla. If you dont want to go the dropper route, do some search on this forum and you will get a decent idea of how much to add and then you can use more/less on your next batch
