An assessment is required following modifications to your vehicle. When must this be performed?

Your answer is correct. In Germany, if you make modifications to your vehicle that affect its safety, emissions, or official approval (like installing other rims, suspensions, or tuning the engine), you must have the vehicle inspected promptly after the change. This immediate assessment is necessary to ensure your vehicle remains compliant with road safety and technical regulations. Waiting until the next official inspection or until asked by the registration authority is not allowed. This rule helps maintain traffic safety and ensures all vehicles on the road meet valid standards right after any significant changes.