It's not a modification if it is strapped in.......did you read the comment from Allianz I think it was.
I've had similar arguments in the past but it all depends on the attitude and policy of the particular insurance company.
Some don't care if you add alloys, leather seats, water tanks, uprated suspension, pole holders, or racking.
Others will refuse to insure if it differs in any way from the specification it had when it left the factory. These are usually the companies that become hysterical if you've changed the brightness of the interior light.
I just don't deal with those types anymore as it's bad for your blood pressure.
You just need a company that doesn't work from a script, listens and is able to make reasonable allowances and decisions.
Gladiator, Adrian Flux, anyone that does non-standard risk.