Yes. You should tell them or you risk any modifications resulting in your insurance being invalid. That said, we've worked with many insurance inspections and their opinion can be boiled down to "When is a modification, a modification?"
i.e. You've put a set of cheap tyres on the car, that aren't approved?
Maybe you've installed a steering wheel cover, is that a medication?
You've installed different alloy wheels or changed their colour?
I think the point is, a small remap to gain a few HP or sticking a turbo on the car or making a V6 into V12 may have different impacts.
What about if your car has been modified before you bought it? Does that invalidate your insurance too?
In any case, it is probably best to ask your insurer what they think.