Total rubbish.
If that was the case, oem part manufacturer would be up in arms.
A modification is something that makes the car more attractive to the thieves or changes its performance substantially.
So, using a chinese oil filter instead of a oe doesn't invalidate insurance.
Differently, a sport exhaust would.
Changing cloth interiors for leather should be reported as a modification because it's substantially different and makes the car more attractive to thieves.
However, insurance companies don't care that you've spent £1000 on leather interior, in case of theft they'll give you the market value.
Unless you declare the modification, agree on a market value and pay a higher premium.
Same for tyres: as long as you stick to the size recommended in your user manual, you don't need to do anything.
The fact that a car comes out of the factory with pirelli tyres doesn't mean that you can't use Michelin.