Note: The information in this thread is no longer current, and has been superseded by the Mod Developer Programme topic.
At the request of germanchocolate, I've created a quick update to Airships that can be modded. You can download it from the usual place
The way that this modding currently works is by selectively replacing some Java classes with ones found in the new "mods" folder. germanchocolate has in fact already created a mod that adds a build queue and an inter-empire relations system!
Right now, the only way to make a mod is to decompile and edit the game's source. As I mentioned in the earlier modding thread, I'll be moving things like module definitions out into data files eventually, which will allow for an easier way to make simple mods.
The main reason for this post is to specify some rules for modders, with the intent of preventing future confusion or disputes: