I understand, but even with a law, it is still a gray area and that's where the original question comes from.
I have also read that one forum member got his gearbox replaced even though this engine had a number of mods known to the dealer. He said his warrantee claim was denied 2 times and on the third time it was approved. I was amazed, he should should definitely go buy a Lotty ticket. On the other hand I have also read posts where they lost out and had to paid out of their own pocket.
This is a risk to me, sometimes you might be lucky and other times you will not.
Maybe you are correct to say the question should be whether or not you are prepared to take Kia to court in the US?
1) If you mod your car, have the money to fix your car. It really is that simple.
2) The dealer can refuse to work on your car in the short term even if you did nothing wrong to your car. If the chance exists that you caused the damage, they can deny work until you escalate the matter within the dealership, then with Kia, then with legal help.
3) Escalating the issue is simpler if your regular maintenance has been performed, your car is well maintained (clean), your car is not modded, and you are polite and INFORMED.
4) If your car is modded, you don't have to convince Kia that the mod didn't cause your damage. You have to convince your lawyer. If your case is weak and not straightforward, it is quite possible that you will not find a lawyer to represent you. The lawyer only gets paid if Kia agrees to a settlement or if you win in court (at least in NC). They don't make a ton of money doing this type of work and will not take work they can't get paid for.
5) Throughout this lengthy process (months), if your car is undriveable or unsafe to drive, you should have alternate transportation. You may choose to fix the car at your own expense and hope to be reimbursed afterwards. See rule #1 in the event that you don't "win."
Fortunately, the overwhelming majority of drivers will never have to deal with this and I hope it stays that way.