While pausing, press all four shoulder buttons (L1+L2+R1+R2) and press the following buttons for the corresponding cheat:

Gain 1000 XP - DOWN, DOWN, SQUARE, X
Level 2 skills - DOWN, DOWN, SQUARE, SQUARE
Level 4 skills - SQUARE, X, CIRCLE, DOWN
Level 6 skills - DOWN, DOWN, SQUARE, TRIANGLE
Level 8 skills - DOWN, TRIANGLE, X, SQUARE
Restore missiles - SQUARE, CIRCLE, CIRCLE, TRIANGLE
Three-hit combo - TRIANGLE, X, UP, TRIANGLE
Four-hit combo - TRIANGLE, X, SQUARE, SQUARE