Reservation for bus to Shirakawago

Hi, I will be spending a night at Shirakawago on the 13 Jan and since it is the light-up event, I was worried that there will be a lot of people going up that day and so I've quickly reserved my Nohi bus ticket from Kanazawa to Shirakawago already. However, recently, I found out about the Mitsuboshi Kaidou Three-Star Route Option Ticket which will cover quite a number of places that I want to go. So my question is this: Should I get the Mitsuboshi Kaidou Three-Star Route Option Ticket when I reach Tokyo on the 7 Jan and cancel my nohi bus ticket and then re-book it using my Mitsuboshi Kaidou Three-Star Route Option Ticket? My worry is that once I cancel my nohi bus ticket, I may not be able to re-book it because the bus is full? Usually how far in advance do I need to reserve the nohi bus ticket? Thanks!