If you want to reveal a second material you would just put a second material on your object. You’ll see that the new texture tag appears to the right of the original texture tag on the object. Drag the original material’s tag (the one with the alpha channel) to the right of the other tag and you’ll be good to go.
The texture tag’s act as a basic layering system, with the bottom layer at the left and the top layer at the far right.