A technical modification to your vehicle means that the operating licence is extinguished. What consequences should you anticipate if you nevertheless use the vehicle on public roads?

You answered correctly. In Germany, if a technical modification to your vehicle causes the operating license (Betriebserlaubnis) to expire or be lost, you are no longer legally allowed to drive that vehicle on public roads. Doing so can lead to three main consequences: you may receive a fine from a public authority because it is an administrative offense; you can get an entry in the Central Register of Road Traffic Offenders, as driving without a valid operating license is a recorded violation; and you risk losing your insurance coverage, since your insurer may refuse claims if the vehicle was not street-legal. This rule exists to ensure that all modifications meet safety standards set by law. Always make sure that any changes to your car are approved and documented to keep the operating license valid.