Unity Terrain Texture Swap...how to?

I am currently using the following function, but it does not seem efficient enough, so i am also looking for a better solution.

 // Load specified texture and only that texture in given terrain
 void LoadTerrain(TerrainData terrain_data, int texture_level) {

     float[, ,] alphas = terrain_data.GetAlphamaps(0, 0, terrain_data.alphamapWidth, terrain_data.alphamapHeight);

     // make sure every grid on the terrain is modified
     for (int i = 0; i < terrain_data.alphamapWidth; i++) {
         for (int j = 0; j < terrain_data.alphamapHeight; j++) {

             // make sure only set layer is visible
             for (int k = 0; k < terrain_data.alphamapLayers; k++) {
                 if (k == texture_level) {
                     alphas[i, j, k] = 1;
                 } else {
                     alphas[i, j, k] = 0;
                 }
             }
         }
     }

     // apply the new alpha
     terrain_data.SetAlphamaps(0, 0, alphas);
 }

http://answers.unity3d.com/questions/285816/change-terrain-texture-and-tree-at-runtime.html#answer-285924

a little upgraded script that allows to change texture without full repainting, e.g. it saves paint map and changes texture.