Can customers with the Deutschland-Ticket and a first class surcharge use first class for a single journey?

An upgrade to first class is available in accordance with the tariff conditions of the nationwide ticketing system (Deutschlandtarif) as a single upgrade, or as a monthly upgrade for season tickets, or within the areas of validity of the transport associations and regional ticketing systems in accordance with their conditions. 

An upgrade to first class is available in accordance with the tariff conditions of the nationwide ticketing system (Deutschlandtarif) as a single upgrade, or within the areas of validity of the transport associations and regional ticketing systems in accordance with their conditions. Upgrade tickets are available for single journeys or on a monthly basis.