Hi, the Modding Manual is a good start:
https://www.transportfever2.com/wiki/doku.php?id=modding

Creating completely separate copies is the correct approach, because modifying existing vanilla or mod files causes conflicts/crashes.

Tracks usually exist as .lua files in the res/config/tracks folders of the vanilla game and the individual mods.

Make your own mod in the staging_area folder. Give it copies of the original track .lua files with new unique names. (Usually authornameorinitials_modname_filename.lua or something.) Then modify the contents of the .lua files the way you want. Be sure to update the name/description fields too so they will be easier to identify in the game menus (because they will have the same icons if you don't make new ones).

Don't duplicate any other files into your mod. Both mods must be loaded in your game because your mod is dependent on the original mod's model, material, and textures files. You can enable them both in any order and there should be no conflicts.


An even better method is to script it in mod.lua postRunFn to create dynamic copies of the original tracks when the game loads, but depending on your knowledge/experience level you might find the above easier.