I made a first release of the modding tool and a mod for loading items made with it:

Here is the tool, it should be possible to extract it anywhere on the disk. It will look for filenames relative to where its extracted, so it just needs the data files to be in the same folder.
http://dionysus.dk/devstuff/downloads/SatelliteReign/SatelliteReignModdingTool.zip

http://dionysus.dk/devstuff/downloads/SatelliteReign/LoadCustomDataMod.zip
And this^^ is the mod that loads customs items. It is to be extracted to the Satellite Reign Mods folder. It contains the mods dll file, a folder with all the item icons and 4 XML files. Two translations files and two items files. One set with the original game data and one set where I added some custom items. They will be ready from when you start the game, the new items. They are a bit overpowered though, but it is to show what can be done with custom items.

There are still some things that needs to be done with the tool and the mod, but I think its ready for people to try it out.

I will be updating this and adding more features. There are quite a few properties that the tool does not give access to yet. Also you cannot change item icons, so you have to copy an existing item and this item will contain all the data that cannot be changed right now. What can be changed though, is what abilities the item gives the user and what effects it has on the user.. they are called modifiers.