Por lo que veo no se puede adiocionar un campo mas (Rafa nosotros no tenemos acceso a programarla como dice Mauricio), en el formulario dice que:
(Gas Station Brands
In this forum you can add, delete or replace gas station brands in your country, please make sure to separate each brand with a comma.
If you want to change a fuel type in your country, please remember that Waze can support a total of 4 fuel types per country (the 4 fuel types most be the most popular/sold fuel types) and please write your reason to replace it in the “Comments”.)
Entonces si seria bueno suplantar el de gasolina Extra por “Taxi”, la mayoria de taxistas siempre tanquean son corriente o gas.