There is no tutorial on replacing RoRBot as it requires extensive knowledge with Blender character rigging, and the character model hasn't changed for nearly a decade. Exporting is the same as any other mesh, except a .skeleton file will be exported containing the animation data: https://docs.rigsofrods.org/tools-tutorials/blender-mesh-editing/
Replacing RoRBot is possible but you must use exactly the same filenames/animation names as the default one:
- File 'character.mesh' (resources/meshes.zip) is the 3D model (source code)
- Material name is "tracks/character" - RoR updates it with multiplayer colors (source code) - if you don't use this name, coloring will not work for you.
- Animation names (case sensitive): "Turn", "Side_step", "Swim_loop", "Run", "Walk", "Spot_swim", "Idle_sway".
Note: File 'character.skeleton' (resources/meshes.zip) is the skeletal animations, but it's name is specified within 'character.mesh' so you can use your own.