Your priming sugar will be a very small addition to the fermentables so the increase in alcohol would also be small. So far in my experience all beers change taste over time....some of that attributed to the beer maturing, some to yeast settling out. For some of my beers that change is happening for only a short time (wheat beers, light colored beers) while others keep changing for a long time (imperial stouts still change for over a year).