How to modify AI (not do the new one)?

[Grani]

Hello,
I wanted to add a few custom units made by me for use for AI players, however, I don't want to create a whole new AI just for this.
I simply want to modify existing Blizzard melee AI to include these units.

Aaand I'm not sure how to do this...
AI editor seems to allow creating AI only from scratch and I can't find Blizzard AI files anywhere that I could load and then modify.

Thanks for help.