Insurance for modified BMW - how to declare mods?

Just got my F30 335i tuned (stage 1) and wondering about insurance. Do I need to declare the remap to my insurance company?

Ive heard that if you dont declare mods and have an accident, they can refuse to pay out. But if you do declare, the premium goes up massively.

How do you guys handle this? Anyone had experience with insurance claims on a modified car?