They do not invalidate your insurance!
I was on the phone to Adrian Flux earlier about something else & asked them. They said that it does not invalidate your insurance & if anything changed legal-wise, they would contact every owner who had them fitted.

Btw..I did read all your reply, but as Martyn wrote, why let the engine get even hotter waiting for the fan to cut in & switch off, when you can drive back the last 5mins off boost allowing cool airflow to help cool the turbo.