You can easily edit the CPU decks.
The main issue is the AI is really bad. I made a little change in the AI so it doesn't do some obvious mistakes anymore (like attaching a basic energy instead of a Double Colorless on Pokémon that need 2 colorless energies to attack). It took me a lot of time, mainly because I'm a beginner I guess.
The CPU tends to put Big Basics that won't attack in front to prepare their Bench.
The CPU can deck out itself with Kangaskhan using Fetch 25 turns in a row while you do nothing.
Some opponents have a Special AI (allowing them to use Pokémon Breeder for example).
Others won't start the duel unless they got 2 basics in hand, some Energy cards, or some specific Pokémon.
I'll document it on Data Crystal once I finish some other projects (Yu-Gi-Oh Dark Duel Stories hack and a Pokémon Stadium 1 / 2 editor)
For the CPU Decks, the format is [Amount] [Card]. For example :
0x30848-0x3086F : Grandmaster Ronald
14 02 04 07 01 3D 02 40 01 5A 01 5F 01 72 01 76
02 B9 04 BC 04 BF 03 C0 02 C1 01 C3 03 C5 01 C9
02 CA 03 D0 03 D5 01 E3
0x14 = 20
0x02 : Fire Energy
=> 20× Fire Energy