I want to create a grid building game i googled for some grid tuts and found this:

1.png
Youtube video with .mfa in desc:
http://youtu.be/1JMzg6206HU

The only thing this tut does is chaning the texture but i dont want to change the texture i want to change the object.
When there is a grass block and you click it it changes into a stone block.
But its a bit hard to i tried a lot of things that are hard to explain in this topic.

So my goal is when you start a new game it creates a 10x10 grass field (tiles are 32*32) and when you click 1 piece
of grass it destroys the grass tile and quikly spawns in a stone block.
I hope somone can help me with this Thanks!