It all depends on how much you change the poundage and how far from optimum your setup is currently whether it will affect your tune or not. I tunemy setup initially by adjusting the poundage and not the rest so any 2-3lb change would have some effect. It would be most notable when bareshafting.

Anyway, since you are doing a string/cable change then re-tuning is happening anyway. Just so you know, just because you go to a heavier arrow does not necessarily mean you need to up the poundage. I typically will setup my arrow for the midrange, 65#'s, and then, like I mentioned earlier, adjust the poundage to tune things up. My current deer hunting rig is 67#'s.