Yes, please, I would like to know. If it's short for Modify, I want to know WHAT you can modify?

Mods are short for "modifications" or "modify" or etc...

As far as "what" we can modify... it's a pretty big list. Perhaps to make it easier we can't:

- Create entirely new areas. We can modify, add, subtract from an existing area.. but we can't make one from "scratch"

- We're limited in model animations.. though there are some experimentations going around ;) New combat animations however are a no-go for now

- We can't add New Feats in a way as the game utilizes them (through level up) however I believe we can "hack" our way around it via scripting

Those are the 3 majors, though I'm sure there's ALOT more... feel free (anyone) to add to/edit the list ;)

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@gandiva, Was there something specific you had in mind?

we can't create new models, except for weapons and headgear, we can, but don't: add new voiceovers, replace prerendered cinematics,

Most of the time, anyway. It take a lot of time, not necessarily for great effect. Only if it's quite a major mod are VOs/Cinematics done, really. Like the M4-78 restoration.

We can't port content from KotOR into TSL or vice versa. It's illegal.

We can't take music from films of a length any greater than about 20 seconds - that's illegal.

We can't make entirely new player models, as they lack animations.

We can't (as yet) add new animations.

We can't discuss porting content.

I think that's all.

You can compose your own music and add it it.
You can render your own Ebon Hawk intro and extro videos for a planet. You can make space battle scenes involving capital ships, Sith fighters, etc.
You can make custom loadscreens.
You can re-texture things to make them invisible or different in color...