What technical modifications to a two-wheeler could result in the withdrawal of the vehicle’s type approval?

The combination of options 1 and 2 is correct because both modifications can significantly affect the safety and performance of a two-wheeler.

1. Fitting customized handlebars can alter the handling characteristics and control of the motorcycle, impacting safety during operation.
2. Changing the wheel/tyre combination can affect the vehicle's stability, braking, and overall performance.

According to German traffic regulations, any modifications that could lead to changes in vehicle dynamics or safety can result in the withdrawal of the vehicle's type approval, which is the certification allowing the vehicle to operate legally on the road. Option 3, installing an identical engine, does not require type approval withdrawal as it does not change the fundamental characteristics of the vehicle. Thus, it is essential to select all relevant options to understand the comprehensive implications of vehicle modifications under German law.