I want to mod the game (Warlords 2.0) thusly:

1. Catapaults, trebuchets, cannon, and artillery function like aircraft. They can "air strike" units one square away.
2. The above units can be captured, ala Civ 3.
3. Nothing can bombard the cultural defense/city wall bonuses.
4. Units can be bombarded to death.
5. Archers have a 1 strength "air strike" ability.

What'cha think and how do I do it?

Wouldn't it be better to ask in Creation & Customization? You'd have to warn them that you can't do it in the DLL, but surely there are many more modding experts over there than you'll find here?

Probably, but would they know how to do it on a Mac?

Probably, but would they know how to do it on a Mac?

The same way as one would do it on windows except that you can't do it in the dll.

It's XML changes, which should be cross platform. Even if someone did the mod for you using Windows, the worst they could do would be to use accented characters in the text files that you'd have to modify or delete to make them readable on the Mac.