To change your skater's helmet and pad color go to Board Editor in the Skate shop. Press select to pick a color. The color in the top-left corner will be the color of your helmet and pads. So highlight that color and press L or R to change it to the color you want your helmet and pads to be.
At the main menu, select "Options" and scroll down to find the "Cheats" option. There are fifteen cheats, but they are all off. To unlock the cheats, play as a pro in arcade mode. Finish all the goals for every level. Each time you do this, another cheat will unlock. Then, go back to the cheats menu to turn them on..