The only tracers you can readily play with are the so called '3D' ones which are drawn within a certain distance threshold.
The farther tracers are simple line vectors, and I'm not aware of them being accessible to us modders.
In my effects mod I include tracers in three flavors the player can choose from. You could take out of that pack just the tracers and have a go at them.
You could start with the simple, straight tracers, as they have the minimal number of vertices to adjust. I do all my 3D model work with a spreadsheet. I graph views in the X-Y, Y-Z and X-Z planes.
If you open a .msh file with any text editor, here you will be concerned only with the [Vertices] section. Each line has 6 numbers. The first 3 are the X, Y and Z positions of that vertex. The other 3 define the surface normal vector, and can be ignored.
Copy the data from the vertices section into a spreadsheet, graph the 3 views to see the construction, then increase the relevant XYZ values to fatten up line.
The long line portion will be straightforward. The 'head' of the thing, representing the round blob that is important for seeing the tracer from directly behind or ahead, is made from 3 mutually perpendicular planes, and requires a bit more care to get right. But all told, the model is pretty simple.
Once you have one model fixed up to satisfaction for one color, you will copy these new vertex data to the other meshes for the other colors.
If you already have the tools required to handle the mesh in a more sophisticated way, I envy you.