AI for custom tech tree

I'm making a senario where the orcs can't build burrows, they have pig farms instead. I make it load orc.ai but the computer does nothing, won't attack me or anything. I'm guessing this is because they're wanting to build burrows first, right? How can I fix this?

thanx

--OK, I could change the burrows into pig farms, but is there any other way around this?

Edit the AI file and replace all references to burrows with references to the pig farm. Look into common.ai for the right names to use.