You can go to the purser's desk and have the tip adjusted if you desire.
Our first cruise was on the NCL Sky and it was awesome! We have also cruised several times on Princess and the service was great on each ship we have cruised on. Princess does the gratuities the same way as NCL.
Some people think that if the gratuity is automatically applied to your account, the service will suffer. I don't think that is necessarily the case. I'm sure no matter which line you cruise, it's possible to get a less than enthusiastic cabin steward. We have been fortunate enough to have a great one on each cruise.