In the normal course of handling a claim, I doubt the insurance claims clerk would look into vehicle mods in a meaningful way, maybe just ask a question and accept your answer. After all, that claim process is focused in gathering detail to determine who is at fault. Obvious mods may be noticed by the assessor and reported back to the claims clerk but subtlety may work in your favour, maybe.
However, crash into a $550,000 super car and the claim is moved up the organisation into more senior handlers or their management where their focus shifts markedly from determining who is at fault to ways to minimise their costs. All clauses are examined. In such cases you will more likely loose your insurance cover and with that potentially your house (as the other parties insurance looks to recover from you if you’re the at fault party - if you’re not at fault it can still be a difficult road to navigate).
Also, if someone is killed in an accident, the police will investigate and they will look at all issues related to vehicle road worthy status and what contributed to the crash. The police report may result in a statement that the vehicle was not roadworthy due to bald large tyres (for example) but that this did not contribute to the crash (due to not being wet, no debris on road, etc). Your insurer will get such a report and how they choose to handle the claim is up to them. The clause is available for the taking but if you are charged by the police, it’s much more likely to be invoked with a sad outcome. In any case, if someone died, you may not need your house as the government may look after your accomodations for some years
Me, i’d want to make sure that everything is above board with my vehicles use so that there are no conditions that would put my cover at risk... no illegal mods and no alcohol or drugs in my system. Guess I’m conservative by nature but others may be happier to sail closer to the wind
And when it comes to legal verses illegal mods, each state has its own rules so it may get rather interesting once you cross the border and are involved in a crash