Is it possible to add a custom shading model to a decal?

Hello,
I created a custom shading model for our project that modifies the received lighting using a texture (plugged into the custom data pins).
To be more flexible and reducing the need of masks, I want to use decals that render with my custom shading model and only place them where I want.

In theory this should be possible, as decals write into the basecolor-buffer before it is passed to lighting, right?

Does someone did this before or has some ideas how to achieve this?

All best

basically what I want is to overwrite the shading model with a decal.