I would like to instantiate different objects (i.e. poker chips with different values) that actually share the same mesh imported from blender. To this end I have copied the assets and changed the texture but all the assets automatically switch to the last texture I choose as they are actually the same entity. What am i doing wrong?
You need to create different materials with different textures. To apply this new material just drag and drop it the the empty space in Inspector view. You will see the material change and corresponding texture will be applied. Now you can change texture associated with this material and all the mesh which use this material will have same texture.