I’m not entirely sure I understand what you’re trying to achieve, but it sounds like you may want to use a material mask to change only certain parts of your material. Are you trying to do this with a dynamic material where you would change it from within a blueprint?
Please clarify where you can with a better description or rough drawing.
Here’s an example of the effect i’m trying to achieve in my project.
The characters would render as an outline around their flat colour sillouhette when they are behind walls or are not visible by the camera. Any guidance towards achieving this would be greatly appreciated!
This can be achieved enabling the CustomDepth feature on the mesh (e.g. skeletal/static mesh). You can look into BufferVisualization to see the content of the CustomDepth buffer. Then you make a postprocessmaterial that colors pixels with an outline and fill. I think the Non photorealistic rendering project has some postprocess materials that show how to do an outline shader.