Brake line change against steel flex: experience, loss of warranty?

Good day, we are currently expecting our new Ceed (used, 1 year old, 17TKm). With its now 13 year old predecessor, we had the rubber brake lines replaced with steel helmet after about 5 years, because I did not agree to the response behavior at all. At the test drive I already noticed that the Ceed is better than the Hyundai in the original earlier, but by far not as crisp on the brake as the Hyundai now with steel helmet. Does anyone have any experience here what this does with the 7 year warranty? I think it’s hard to assume that it will go out at least for the brakes. Or would that affect even more?