An interesting point though; assuming you should declare any mods to your insurance company what about those the general public that replace brake pads with aftermarket ones from Halfrauds, or an exhaust from KwikFit, or change from the manufacturer's fitted Bridgestones to Falkens, or their local garage fits pattern track rod ends that aren't made by the original car company. My dad's Volvo has aftermarket pads, discs, exhaust, tyres etc - not performance upgrades as he only got them to save paying Volvo prices, but they differ from manufacturer's OEM stuff; should he tell his insurance company? He hasn't and therefore, technically, they could wriggle out of a claim, but that probably also applies to 60% of the cars on Britains roads - are they all technically uninsured?
Who decides what makes a change from OEM into a modification - be interested to hear from the insurance guys on this issue as I've had the same conversation in the pub many a time.