Replace the values in the desired SAVE file
Grandia 2: Cheat Codes (HEX) Free Download
HEX cheats:
65535 Gold:
On line 0040, change the current value to FFFF
65535 Special Coins:
On line 0044, change the current value to FFFF
65535 Magic Coins:
On line 0048, change the current value to FFFF
Keep in mind that the game has a limited limit on adding coins using this code (the second time it may not work if you start the game before)