Oh! That sounds bad, but I think you didn't read the coverage policy thorough that either they will offer coverage in the case of this kind of modifications or not. To avoid such problems, I always read the policy correctly and usually prefer to go with fleet insurance plans. These days, I am comparing fleet insurance quotes from sites like this ( https://www.comparefleetinsurance.co.uk/
) for my jeep and RV but yes, I am not going to OK any policy blindly.
For now, I think you will have to rely on the instructions of the insurer or have a choice to get that specific insurance as well.