It all depends on the dealership, to be honest. If they're a bunch of ego-driven dickbags, they'll find any way they can to blame you for the damage to protect the manufacturer. If they get along with you, they'll turn a blind eye here and there if your mod clearly doesn't cause the problem that you might be having.
Having said that, BMW is considered a higher-end brand out here in the States, so they treat their customers much more leniently, promptly, and with much greater courtesy. In fact, most name brands do: it's part of the reason people go for name brands. They know some cheaper Mercs and BMWs are absolute trash cars, but because of the brand, they know they'll be taken care of and don't have to worry about it.
Kia is only used to deal with economy vehicles and buyers, so they've got a lot of work ahead on learning how to deal with Stinger owners starting at how their dealerships handle them. They do seem to be giving dealerships reminders that Stinger owners are "VIP", but it has yet to sink into the Kia dealership I have to go to (because it's literally 2 miles from my home).
It's all luck of the draw, but if you want to mod a car because it genuinely brings you joy, I say do it. I wouldn't drive a car I don't want to every day, that's for sure, lol