Five lives:
Hold Up + A + B and press Start at the player selection screen. Note: This code may also be re-activated at the game continue screen.

Level select:
Press Down, Up(2), Down, A, B(2), A at the player selection screen. Game play will begin with ten lives after a level is selected.

Extra lives:
Start a two player game and play all the way to the end of level 1-1. Do not enter level 1-2 yet. Instead, turn on player two and use up all of his lives. Continue the game as player two, then repeat this process until all of player two's continues are used. Then, continue the game as player one. However, if all the pods on Level 1-1 were broken, you will have eight more lives and will have earned more through the points awarded while defeating player two. Two more lives can be obtained by going through level 1-1 again.