Check out the OpenSWE1R project.
I've started the project last year and we create an open-source version of the games code.
We also analyze how the internals and file formats work.

We already have tools to work with various file formats, including models / textures, sprites, splines and savegames.
There is also information how certain aspects of the game work internally.
Unfortunately, at this point in time you have to know how to program / develop software to use / gain anything from it (and a good bit of reverse engineering knowledge would be preferable).

The podracer data is actually stored in the swep1rcr.exe, so it's hard to modify.
However, there is also a debug menu in the games N64 version.
We've documented how to open this menu on the PC version with a bit of trickery. It can be used to change podracer handling parameters.

Information is on GitHub: https://github.com/OpenSWE1R
Also join our gitter chat: https://gitter.im/OpenSWE1R

Attached is a screenshot from earlier today. We are currently working on supporting model and texture exporting from the game.
We'll work on re-importing those files at some other time. It's a lot of work and there's very few actively people working on this (actually only 1 until last week: me. Now we are 2).