No problem. Most people would never bother telling their insurer in the mistaken belief that even though the bits stuck on are original manufacturer items, that it might not make a difference. If it didn't come on the car as standard, then it aint standard if you put it on after! By the way, this doesn't cover tyres of the same size as was on the car, it would be ridiculous to suggest you must inform your insurer if you swapped from Goodyear to Pirelli for instance!
Sadly, experience taught me a long time ago, that some insurers will do literally ANYTHING to avoid paying out if you need to make a claim. That's why it isn't always the best option to choose the cheaperst insurer out there either come renewal time, just read through their T's&C's. But that is the subject of a whole different thread!