Development issues in minecraft packages for unity 3d version

Hi. My questions are directed to those who have played Minecraft. I am currently involved in an effort to create Minecraft packages in Unity 3d versions. So far, I have been doing fairly well but there are still some things I couldn’t figure out. One issue I’m facing is on how to add more textures into the main texture when a player clicks to destroy blocks so he could see how much damage is left. I would appreciate if someone could help me along in the development.
