How do I change the symbology of the terrain line in cross sections without modifying the terrain file?

I have a terrain, geometry, corridor and drawing-container i separate files and I am cutting cross sections using Named Boundary.

The terrain has a Feature Definition (and thus Element Template) making it grey:

The drawing container file has terrain, geometry and corridor attached to it. 

When I cut Civil Cross Sections, the terrain shows as a grey line:

I would like the terrain line to be green instead.

So in the Default Model in the drawing contailer file I select the terrain and choose Overide Symbology and another Feature Definition.

The new FD uses this Element Template with Level Symbology of a level with green color:

But the terrain line in the cross sections does not change.

Changing the Override Symbology for the referenced Terrain file does not work either.

I have tried replacing the Terrain file with a copy where the Terrain has a "green" Feature Definition. This works.

But I do not want to keep a number of copies of my terrain for different display purposes.

So am I misunderstanding how to use the Override Symbology and how can I change the symbology of the terrain line in the cross sections?