http://forums.amplitude-studios.com/showthread.php?9258-Tutorials-for-Modding-ES

Some games lend themselvrs well to modding while others don’t. Those that come as a monolithic executable are practically impossible to mod; those with many data files range from “requires special tools” to “my cat could do it with Notepad and MS Paint”. Without more technical details about that particular game, it’s hard to tell what is required since it’s that variable. From what I’ve seen, ES requires hefty skills to mod.

Personally, I favor games that have editors either included or commonly available. In that vein, I’m currently grooving to Shadowrun Returns which is basically an editor that just happens to come with a decent premade story that’s solid in it’s ownright. Much easier to create content.

I made some ships for Freespace 2, but nothing in the way of scripting/coding

I did a bit more digging, and you may not like it.

How well do you know XML programming? XML code-wrangling really is the only way to mod ES.

In general modding a game is like modifying any other computer program. Unless it comes with another program (like a scenario editor or so) that helps you to make changes, you will need to learn about how the game works.
Pretty much any game will consist of a set of data and some operations that work on those data. You’ll need to learn how the data is stored and in what format, and how and when it is accessed or modified by the game logic.
Lots of games (including, apparently, Endless Space) can be modified by just messing around with the data files they use (in this case a collection of XML files). Others require that you learn one or more programming languages (for example, you could mod certain aspects of the Ryzom client in Lua, but you’d need to know C++ to mess around with the core engine.) You’ll also need to Use the Force and Read the Source- that is, get the source code for the game and read through it to see how it works. Most large and complex games make use of lots of libraries. You won’t need to know about them all, but some of them will be relevant to what you are trying to accomplish.
The first one will be the hardest.
Don’t be afraid of XML, by the way. It will be familiar to you if you know HTML (in fact, later versions of HTML are XML.) The core language is easy to learn. In order to use it to mod a game you will need to learn what a DTD is (a Document Type Declaration) and know the ones used in the game’s XML files.

Most of the modding I’ve done personally has consited of fucking around with XML codes and changing values for things, never anything too serious unless the game also had a dev kit.
I’ve been hooked on Endless Space for the last two weeks :P

I had a lot of fun modding Saint’s Row 3 (and that game, when played drunk, is quite funny, probably funnier if you’re taking something not legit), Mafia 2 required tools from third parties same as SR3 – not sure about how you’d go about modding the game you suggested but with jerv saing xml…damn. xml isn’t a great deal of a challenge once you’re used to it, but it does get to be a massive drag.