Bring up the start menu and press "select" exactly 16 times (no more, no less) and a small square will begin to flash. Hold down the "A" and "B" button and use the control pad to change: Your number of lives, your number of coins, hearts and even have much time you have left.
Note: You must press "A" and "B" at the same time to move the square. Move it to the small Wario-face to change the hat you're wearing. By holding "A" while changing hat, you can jump in mid-air. Change hat again to jump even higher.
Change any of the numbers on the display and get a better Hat
Added 8 Feb 2005, ID #3268
Pause your game and press Select 16 times to make a cursor appear on your number of lives. To move the cursor to any number on the screen, hold A or B and press Left or Right. To change a number, press Up or Down. Give Wario a new hat by placing the cursor over his face in the bottom-left corner of the screen and press Start to return to the game.