Instantiate a prefab and access sub-mesh material

Hélo,

Unity noob here, I may have started with the wrong project :)

I'm trying to create a small lighting simulation app. My projector is made of several meshes. I made a "Projector" prefab that I can instanciate with an Empty Object containing the following script :

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class projector_instancer : MonoBehaviour {
 
     public GameObject proj_prefab;
     private GameObject proj_array;
 
     // Use this for initialization
     void Start ()
     {
         for (float x = 0; x < 10; x++) 
         {
             for (float y = 0; y < 10; y++) 
             {
                 // Create the clones
                 proj_array = Instantiate (proj_prefab, new Vector3 (x * (float)1.5, y * (float)1.5, 0), Quaternion.Euler(90,0,0));
 
                 // Rename the clones
                 proj_array.name = "Projectorl";
             }
         }
     }
 }

"proj_prefab" is supplied via Inspector, and contains the meshes making my projector.

Ok, now the tricky part. I would like each of the instantiated prefab to receive two textures, each one on one of the mesh they are made of (these projectors are actully LED matrices on a moving head). Later they also have to be stretched/translated so that each projector displays the part of the texture it's supposed to display.

Thing is : I have no idea how I should provide those textures to my prefab. I guess I'm lacking some Unity knowledge...

• should I create a Material public var in my Instancer script, and assign/offset/scale the texture in the same loop that instantiates ?

• should I assign my material to my prefab and do the offset/stretch thingy in another script ?

I'm totaly lost here, any help would be greeeeeaaatly appreciated :)

Thanks !