Yeah, don't do any of that if you like being insured.
Look at it like this: You have an accident and end up piling into a load of people waiting at a bus stop. They all survive, but all need special care for the rest of their lives. The bill is going to be in the region of £10,000,000. Do you not think the insurer might spend another £200 getting the ECU checked? I agree that if it's just a minor ding then no, they probably won't check, but I wouldn't want to stake every penny I own on it.
Not telling your insurer about every single mod is just dumb. Read the contract.