What alterations can result in the permit for use (Betriebserlaubnis) being cancelled?

You chose correctly. Installing an engine with a different power output or fitting fairings can both affect the safety, emissions, or functioning of a vehicle. Such modifications often require official approval because they might change the basic characteristics approved in the original permit (Betriebserlaubnis). If these modifications are not properly registered and approved, the permit for use can be cancelled. Simply installing a radio does not impact vehicle safety or operating characteristics, so it does not lead to cancellation. Always ensure any technical changes to critical vehicle parts are officially authorized before use on public roads.