If you have an insurance certificate, the insurers WILL pay out for third party losses in the event of a claim no matter what you may have done to the car. This is a legal requirement they can not and will not wiggle out of.
If you have undeclared mods, they may...and I say may, even this is not certain...not pay out for your own damages if you are insured fully comp.
However, lets be serious here for a minute. You crash your car....if its minor, you exchange details with the other party and everyone carries on. If you properly spank it then they may send an inspector to check the car, who is more interested in deciding if it is an economic write-off or not. If you have a supercharger sticking out the bonnet, racing slicks and a roll cage, he may decide that perhaps its been modified and requires further action, but he is not going to be poking around the wiring loom to your fuel rail and MAF looking for wiring that is in slightly different trunking to the original stuff. He probably couldn't point out these components if you ask him to anyway - he will not be a Freelander specialist, just a general vehicle inspector.
If the Synergy unit gave the kind of power gains that mean you could come off a roundabout in a 4-wheel drift, clip a kerb and barrel-roll it 5 times down the high street before going through the window of an antiques shop, then attracting that kind of attention might warrant deeper investigation, but the rear world gains from a Synergy just are not going to be noticeable to anyone, even a crash investigator, after you have had a corner to corner knock with someone pulling out of Tesco's carpark.
