[Seihen]

Why isn't there an editor? 'Cause you haven't made it yet, buddy! 
Let us know when it's ready, so the common person can use it and edit things a little easier.

[mantidactyle]

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