Overriding shaders of Terrain Grass in 2019.2

Hi

My Project use 2019.2 not using SRP.

I'd like to modify the shader that is used to render the grass-meshes that I paint on the terrain with the Unit tools.

Here's what I tried:

Downloaded the built-in shaders for the correct version

copied the shaders into the Assets-folder

Tried to modify the shader "Hidden/TerrainEngine/Details/WavingDoublePass"

I remember it working in a 2018.x. but 2019.2 not working.

Questions

1. Is built-in shader overriding not supported in 2019.2?

2. Is there any way to fix WavingDoublePass?

3. Does the update plan have the ability to set grass material like terrain material??