> What is your understanding of the Act and its limitations

They can deny a claim. You can challenge that, they will need to prove the modification caused the defect. They cannot void your warranty, in whole or in part. The most they can do is make a note of your modification and then use that as a reference going forward to deny individual claims as they happen.

You might argue that they are likely to win those claims, because they have the engineer who will show up in court to explain why your modification was the problem. On that I'd agree. But they'll have to do that for every claim they deny (assuming you take them to court).