Using an all-cards save doesn’t break the game — it just turns Power of Chaos into a deck-building sandbox rather than a grind. Since the games are offline and no longer supported by Konami, there’s no risk of bans.
For :
An "All Cards" save file does exactly what it says on the tin: Yu-gi-oh Power Of Chaos All Cards Save Game
For users possessing the file, the standard implementation is as follows: Using an all-cards save doesn’t break the game