For what it's worth, here goes.
The files to work with are in the /Modules folder with the ".rim" extension. There are a series of large and small files for every area. In general, the larger files are the ones to look through. I'll use my first search as an example.
The file "tar_m02ac_s.rim" covers the first area on Taris when you leave the apartment. It contains information about tons of stuff (naturally) but what I was interested in was the item list for Kebla's store (Zelka's med store is also in this file).
Each item is listed once if it's infinite or just 1 is available (don't know where the quantity flag is at this point). If there are a given number of items, they'll be listed X number of times.
The code will look like this:
xxkeblastore..g_w_stunbaton01.g_w_qtrstaff01 etc.
It's important to note that the period just before each entry is a hex value equal to the number of bytes the item name occupies. This is important because whenever I tried to insert an item with a larger or smaller lable, the level was only partially loaded (no doors, no people... ). I'm sure someone else could figure a way around this, but it won't be me.
Anyway, it works fine the way I've been doing it.
A file in the root folder, "chitin.key" contains - as far as I can tell - the lables for every object/item in the game. The items you can add to a store inventory generally start with g_a_ , g_i_ , g_w_ .
Since there are hundreds of items in the game, and I've only been working on this for part of a single day... well, the list is coming along.
The key to making this work is that you have to edit the rim files BEFORE you ever enter the area. The game draws resources from the rim and compiles them with other info into a ".sav" file. These files go by the same name as the .rim, but are different in size and the code isn't clear like it is in the .rim. If you're testing, you have to delete the cache files so the game has to draw upon the altered rim once again to enable any changes.
I haven't had time to test whether or not saving a game, then deleting to cache will still allow for changes. With the ungodly size of the save files, I'm guessing they contain enough data that the game doesn't have to access the original .rim file again ( someone please correct me if I'm wrong).
This is basically it. Pretty simple, but I've found some interesting things I had never seen in the game before. Insta-kill pistol (on hit: Instant death DC 100), some armor I don't ever remember seeing (and I went out of my way a couple of times to collect all of them... I thought). And if anyone is wondering about Starforge robes...
If you have the time, the game, and the desire it's worth a go.