With the native C4D renderer(s) it is possible to do the following:
Add a base texture to a model with, say, Color (the C4D way to say: It's a diffuse texture!) and Bump active.
Add another texture tag with just Bump active and activate "Mix Texture".
This way you get another layer of, for example, scratches mixed with the base texture.
Would this be possible with Corona, too?