Also you don't have to make seasonal variations of each texture, you can just reference what you hvae in your list.
So, in my little test route using the same methods in earlier posts I made a Snow, Mud and meadow texture sets. I then referenced them on the season slots for mix map 1.
So, where every the grass is sprayed, in spring there will be a meadow, Autumn there will be mud and in winter there will be snow.
A good example of this in RWs is where we have a ploughed field in Spring, Cornfield in Summer, mud in Autumn with snow in winter. This really does help give your routes a different feel when driving in the different seasons. (Of course if you have a procedural grass texture you must take into account the changes and make season variations of the grass. (look out for further posts))