SAU.NSW had a Tech Arvo at Syriops Engineers and we were told that if you're at fault and the mods are responsible then your car may not be covered. The car would be covered if you have an Engineering Cert and the mods are listed.
If you're not at fault of course your car is covered; but your mods are not covered if damaged whilst not listed on the policy.
Primarily for insurance purposes, have all mods listed. For defect clarification, get an Engineering Cert and if you want a fully built engine covered by insurance, tell the company about that too.
Insurance premiums don't go up too much with mods added to the policy.