How to replace and find object in mining game?

Hi everyone, i'm making a small game like mining game in Pokemon Diamond. Sorry for my English if i mistake somewhere.
I create map like the below picture, but i got stucked at making the ground side when i use hammer or pickaxe to hit it.

if it just a small rock, i can use tk2dtoolkit to change sprite ID and tag to become other rock layer, but the point it also make 4 square in the next change too (like the above picture, when pickaxe hit the rock, it affect to around ).
so how can i replace many square in one time with a hit?
And when i hit 3 rock layer, it will show the "origin" ground and random item under this. I still not found the way the find the item when remove the rock layer above
so pls help me

 

I guess you're using the 2D Toolkit from the asset store? Then the 2D Toolkit forum is probably a better place to ask specific questions: http://www.2dtoolkit.com/forum/
There's also a Unity forum thread: http://forum.unity3d.com/threads/2d-toolkit-2d-in-unity-made-simple-released.93287