tile_layer_depth

Moves all tiles at a given depth to a new depth.

tile_layer_depth(depth, newdepth);

Argument	Description
depth	The current depth of the tile layer.
newdepth	The depth to change the layer to.

Returns: N/A

With this function you can change the draw depth of a whole layer of tiles.

if change
   {
   tile_layer_depth(10000, -10000);
   }
else
   {
   tile_layer_depth(-10000, 10000);
   }

The above code will set the depth of a tile layer depending on whether a variable returns true or false.