Question

I am able to update the tile once it is pinned, but not when it is not pinned.

This is the code and I am not able to understand where the problem could be. I appreciate if somebody who played extensively can help me out.

ShellTile primaryTile = ShellTile.ActiveTiles.First();
ShellTile tileToFind = ShellTile.ActiveTiles.FirstOrDefault(x => x.NavigationUri.ToString().Contains("TileID=2"));

            StandardTileData newTileData = new StandardTileData
            {
                Blah; //Setting the background 
            };

            if (primaryTile != null)
            {
                primaryTile.Update(newTileData);
            }
            else
            {
                //test if Tile was created
                if (tileToFind == null)
                {
                    ShellTile.Create(new Uri("/MainPage.xaml?TileID=2", UriKind.Relative), newTileData);
                }
                else
                {
                    tileToFind.Update(newTileData);
                }
            }

Answer 1

As I remember, main tile is always exists (even if it not pinned), so primaryTile is always not null. So, your secondary tile is never created with your code.