How to replace the build detail mesh grass for a change in weather seasons

Hi folks! Sorry about my English. The question is. The game is changing seasons. Mesh Prefabs parts are replaced depending on the season. This code works fine in the editor. There is no change in the build. At change of a season in a runtime the grass disappears. Thanks for any help!

public class Season_terrain : MonoBehaviour {

public Terrain terrain;
public GameObject[]    Detail_go;

public bool Winter, Spring, Summer, Autumn; 

update ()
    Create_season( Detail_go[0])
    Create_season( Detail_go[1])
    Create_season( Detail_go[2])
    Create_season( Detail_go[3])

void Create_season(GameObject[]  Detail_go)
 for (int i = 0; i < terrain.terrainData.detailPrototypes.Length; i++)
                Grass_w *= new DetailPrototype();* 

Grass_w.prototype = Detail_go*;
Grass_w.usePrototypeMesh = true;
Grass_w.renderMode = DetailRenderMode.Grass;


The question is a little older but anyway: editing the prototype array this way does not work. You’d rather copy the prototype array to your own variable, replace the details in there and afterwards, reassign the whole array to the terrain - see this post: