Dunno if there's much interest in this, nor have I quite obtained clearance from tptb that it's 100% okay to discuss all of it in detail as there's one particular thing I need to clarify; but apart from that potentially gnarly issue the rest of it is fairly uncontroversial stuff.
Obligatory warning: MODDING IS AT THE USER'S OWN RISK! Your game could become unstable and your saves corrupted and smelly Gorgombert might gush out of your PC's USB ports. You have been warned.
Anyway, that aside, it does have some potential for modding even though apart from my own general meddling there doesn't seem to be much if any of it about.
Part of the problem is that the game doesn't load loose files nor additional DV2 archives, at least not without some incantation that I'm unaware of. And the contents therein are pretty much entirely stored in NIF format, which is a potential headache as it's a binary format, or rather it's a whole family of binary formats which vary from one game to the next and whose proprietary nature often means that the only understanding of their internal format is someone with a hex editor, a lot of time ant patients and probably as much trial and error.
From my perspective that means that modding is currently limited to modelling and retextures. Of the two, modelling has been the more straightforward as Blender 2.49 can read its NIFs directly, and can write them after a fashion, at least once I'd mangled the export script (which I shall upload somewhere, though it would probably be at least polite to check with the original author first). Getting the exported NIF into a format the game is happy with is easy enough and I'll explain in detail in a later post.
Textures are more fiddly, which seems surprising as retexes are the usual basic modding you do when nothing else is really accessible. The reason they're fiddly is that "everything is a NIF" approach, which seemed pretty bloody-minded to me but having finally developed a basic understanding of DDS files and exactly what the NIF contains I now understand why it's a thing: to be used effectively and efficiently, the DDS needs a fair bit of meta-data that the DDS itself doesn't include. The NIF is a nice handy way of storing it consistently. Provided you have something that can read and write its particular format, that is. Until recently I've been creating "FrankenNIFs" by sellotaping file fragments together but have finally written a script to do it properly. That can be made ready for public consumption without too much effort, the only minor snag being that I don't really "do" Windows, I'm a Unix hacker, so it requires Cygwin or a handy Unix/Linux box to run.
If I'm feeling adventurous I may attempt to analyse how the config files work, which are a sort of XML-in-NIF-format thing, though tbh I am not very optimistic: I'm not sure I have the ability, patience nor fortitude, but we'll see.
Anyway, I shall describe the various things I know are possible in more detail a little later.