Remove material slot via Unity Script

Question

I have a lot of duplicated objects, and I need in editor, not in the game, remove specific (18) material slot. Remove not material in slot 18, but remove slot 18. Manually, by hands, it can be done using this button:

All objects that I need to remove slot from has the next mutuals:

1. Contain "_lod" in the name;
2. Have the same mesh, with the same GUID

I did not find how to get GUID of the given object, so the search, probably need to go by name.

I have never scripted Unity, I even did not write in C# (although I write in C++).

What I done so far: I created an empty game object and assign cs script below to it as a component. DestroyImmediate(myMaterials[18]), works almost that I need, but it removes not the slot, but the material on it (and automatically creates default material). I need to remove exactly the slot.

LookAtPoint.cs:

using UnityEngine.SceneManagement;
using UnityEngine;
using System.Collections;
using System;
using System.Collections.Generic;

using UnityEditor;
[ExecuteInEditMode]

public class LookAtPoint : MonoBehaviour
{
    void Iter(GameObject gameObject) // Itterate children
    {
        for (int j = 0; j < gameObject.transform.childCount; j++) 
        {
            GameObject a = (GameObject)gameObject.transform.GetChild(j).gameObject;
            MeshFilter viewedModelFilter = (MeshFilter)a.GetComponent("MeshFilter");

            if(viewedModelFilter && viewedModelFilter.mesh && a.name.IndexOf("_lod") != -1) // check if object has mesh and it's name contains "_lod"
            {
                Material[] myMaterials = a.GetComponent<Renderer>().materials;
                if(myMaterials[18].name.IndexOf("Подоконник")!=-1) // not neccesary check if 18s slot has "Подоконник" name (actually now it is already "Default-Material")
                {
                    DestroyImmediate(myMaterials[18]);
                }
            }
            Iter(a);
        }
    }

    void Start()
    {
        List<GameObject> rootObjects = new List<GameObject>();
        Scene scene = SceneManager.GetActiveScene();
        scene.GetRootGameObjects( rootObjects );
        
        for (int i = 0; i < rootObjects.Count; ++i)
        {
            GameObject gameObject = rootObjects[ i ]; // get root objects

            for (int j = 0; j < gameObject.transform.childCount; j++) // enumarate them
            {
                Iter(gameObject); // iteratevely process the children 
            }
        }
    }
}

Answer 1

So, as @DMGregory pointed in comments, instead of destroying material, the element of the materials array with needed material should be removed, and new, resized array should be set as component:

using UnityEngine.SceneManagement;
using UnityEngine;
using System.Collections;
using System;
using System.Collections.Generic;

using UnityEditor;
[ExecuteInEditMode] // for running in editor

public class LookAtPoint : MonoBehaviour
{
    void Iter(GameObject gameObject) // Itterate children
    {
        for (int j = 0; j < gameObject.transform.childCount; j++) 
        {
            GameObject a = (GameObject)gameObject.transform.GetChild(j).gameObject;
            MeshFilter viewedModelFilter = (MeshFilter)a.GetComponent("MeshFilter");

            if(viewedModelFilter && viewedModelFilter.mesh && a.name.IndexOf("_lod") != -1) // check if object has mesh and it's name contains "_lod"
            {
                Material[] myMaterials = a.GetComponent<Renderer>().materials;
                if(myMaterials[18].name.IndexOf("Подоконник")!=-1) // not neccesary check if 18s slot has "Подоконник" name (actually now it is already "Default-Material")
                {
                   Material[] aa = new Material[24]; // new array that will be assign. 24 because current length is 25

                   for(int i = 0; i < 24; i++) // fill new array by existing, except 18' element 
                   if(i < 18)
                     aa[i] = myMaterials[i];
                   else if(i >= 18)
                     aa[i] = myMaterials[i + 1];

                   a.GetComponent<Renderer>().materials = aa; // set new array
                }
            }
            Iter(a);
        }
    }

    void Start()
    {
        List<GameObject> rootObjects = new List<GameObject>();
        Scene scene = SceneManager.GetActiveScene();
        scene.GetRootGameObjects( rootObjects );
        
        for (int i = 0; i < rootObjects.Count; ++i)
        {
            GameObject gameObject = rootObjects[ i ]; // get root objects

            for (int j = 0; j < gameObject.transform.childCount; j++) // enumarate them
            {
                Iter(gameObject); // iteratevely process the children 
            }
        }
    }
}

Summarizing for newcomers like me:

1. In assets, create C# script with code above (notice, that the file name and class name should be the same);
2. Choose any game object on the scene, and open its properties window;
3. In properties window click Add Component at the bottom (scroll might be required);
4. Find and choose the ealier created script by file name;
5. By adding the component, the Start method will be called, so that's it;