For invulnerability, start a new game and pause immediately. Press A, B, X, Y, Right, Left, Up, Down, Left, Right and the earth will be in good hands.
Change the CloudsThe Not Really Much of a Cheat cheat: In the normal demo sequence, the ships are flying over some nice looking clouds. On Controller 2, press and hold Up and Start. Then hit the RESET button on the SNES. Keep holding until the demo. The clouds are different.