[Help] How to stack Gold Goblin Coin and Rena?

Hello i want to make Gold Goblin Coin and Rena to be able to stack.
Example:
10 Gold Goblin Coint or 199 Gold Goblin Coins.
9 Rena or 999 Rena.
in IGCN season 9.
What i need to do or modify?
I tryed to modify IGC_ItemList overlap but still i cant stack them ..
Thanks.

I modify client files, now i can put 1 Gold Goblin Coin on another but now the question is another.
How to see how many Gold Goblin Coin i have in invetory because it doesent display how much coins i have collected?