So here’s what you need to do once you have you LPG or CNG kit fitted in your car. You should get it endorsed in your RC book or the registration card a registration book whatever it is called in your state. Once it is got updated or endorsed in the RC book you should inform the insurance company about it and get it endorsed in your insurance policy also. Basically it is a change in fuel which is quite a big change. For the insurance company specifically, a few email exchanges and a copy of the RC book should do the work.
Please ensure that you do it otherwise you might find difficulties while making a claim.
Cover yourself with right car insurance policy. It will support you financially during unfortunate scenarios.