Now is not posible to use priority filtering by type of traffic,
But what you can do, is using API accounting and simple queue type, create a sector in mikrotik, for example, 30Mb sector. Then when you asign the tarif in customer services, you must select the router and that sector. You can do it with diferent tariffs with diferent priority(High, Normal, Low), all of them in same sector and router. When the total amount of speed is the maximum in that sector, the priority will be applied.