There is a current error in the file name, same thing in the archipelago. You need to rename the file to have an exact name. Here in this case it should be renamed to exactly season_mod.smod. (In the archipelago there is a second link that will work fine)
This mod is old, and kinda neglected.
Ideally, it should be split based on biomes.
So a player would only see the snow version of the items in the temperate biome, as it is the only biome with the 4 standard seasons (winter,autumn,spring,summer).
Other biomes should have different seasons with different behaviors, like desert having only two seasons (dry, rain) or archipelago having 3 (summer, rain, wind)