Mesh with multiple maps/textures, how to display and swap?

I have a character mesh where I have taken the main texture map, and broken it up into 4 pieces. I want to be able to modify and change the texture pieces in real-time (like one might do in a character customization screen).

I know I can use “Material.mainTexture” to change the texture of a mesh with ONE texture, but how would one do it with 4 materials/textures on one mesh?

Materials: Unity - Scripting API: Renderer.materials

Textures: Unity - Scripting API: Material.GetTexture and Unity - Scripting API: Material.SetTexture

The propertyName used in these texture functions is the name given to the texture in your shader.