@RevNev, one normally buys insurance because one can't carry the loss of a crash (if they are at fault or if the other at fault party isn't insured and has SFA assets one could go after). So failing such wealth which provides the ability to self insure, us mortals purchase insurance to protect ourselves.
Insurance companies policies are complex beasts to fully understand but they do provide many out clauses where the company can choose to deny the claim. Your vehicle being unroadworthy is just one such clause. However, it's a reputational balancing act in part as they don't want to be known as the insurance company that never pays out but to think they would always pay out is foolish.
Their insurance assesors, atleast the ones i've met, are not idiots. They work within the ruels and constrants dictated by their employers. They know their cars, and know what a RVD is. So they have documented evidance of what is optional on each vehicle variant available within Australia. To think they don't know their cars or can't find out about what's standard or optional is also foolish.
It all comes down to whether it worth their effort and any potential reputational damage for them to look for a reason to denying a specific claim. And i'd say they'd spend more effort and have senior assessors and claim managers handling your claim, with fervor, should you crash into a house or exotic supercar, resulting in $500k of damages (or whatever their internal threshold is set at).
So, if you are in the unfortunate situation of being the cause huge $$'s of damages, you are in essence betting that the assesor is an idiot, the senior insurance claims managers doesn't know the clauses they could use to deny your claim and that they are unwilling ito excersise such clause. Your also betting your illegally modified car will garner you some sympathy among the public should Tracy Grimshaw give a toss and actually put your plight on TV for all to see. To be clear, what you may be betting here is your house.
I can only summise you are conflating brake modifications such as fitting Brembos to SS commodore (which require engineering approval else they are illegal and thus the vehicle is unroadworthy) with replacing a rotor with dimples, slots or holes (but is otherwise the same size so doesn't require engineering approval and is thus legal and roadworthy).
Rules are a pain, but ignore them at your peril.