You will be committing fraud and--besides any fines that could be imposed by the government if this comes to light--you could invalidate your insurance coverage. If you register your car at your friend's address, you have to use that address for insurance purposes. But if you lie about where a car is actually located or based when you apply for insurance, you will invalidate the coverage. (And if you ever have an insurance claim, or someone sues you for an accident or injury, with all the paperwork and investigation, your actual address will come out.) Therefore, you could deny yourself the protection of insurance.