To be able to play as the Japanese characters in the game, first you must have beat the ENTIRE Vs. Mode, this means all the N.A. characters + the Japanese characters (or use the 2GSH cheat). Once that is done, start a game in Stroke, Match Play, or the 9-Hole Par 3. Select a character with the clubs/balls you want if necessary. Press Select 3 times, hold Triangle, then press X. You should have the Japanese character equivalent of the N.A. caracter i.e. by doing this with Sam hi-lighted, you'll get Kumi, while with Gex, you'll get Vader. For left-handed Japanese / N.A. characters, simply hold Square, then press X. If you want the Japanese caracter left-handed, hold Triangle + Square, then press X. Note that on the End Game (Stats) screen, if you selected Kumi, she appears, but if you choose any other Japanese character, one of the N.A. characters would take its place, and most likely it won't be the N.A. character you choose for the Japanese character equivalent.
Quick Reset
Press L1 + L2 + R1 + R2 + Select + Start while playing the game.