While the swing meter is on-screen before hitting the ball, press L2 + R1 + Triangle. Press Left or Right to change the ball's shape.
At the main menu, press L1, R1, L2, R2, L1, R1, L2, R2. If you entered the code correctly, you will hear a sound. Repeat the code to select various sound selections.
To get all golfers in stroke play use this cheat at the main menu:
L2[b], [b]R2, L2, R2, then Up, Right, then Down, then Left and finally R1. If done correctly you should hear a sound.
At the character selection screen, highlight a golfer, then hold L2 + Select and press X.