[Darvin]

Big files weren't source code, though; they were definitions and scripts that would be used by the source code. You probably wouldn't be able to understand the source code at a level where you could actually make meaningful changes.

Releasing the source code and allowing for its modification has almost never happened. In fact, there are only a handful of source code modification projects in the history of gaming that have ever been successful, and most of them were in the early days of internet gaming when they were doing something like modding in multiplayer support because the devs didn't see it as a priority.