Allows easy temporary swapping of materials for highlighting i.e. different status of the GameObject (think building systems, obstructed red material, valid green material, placed restore default materials).

MaterialChanger.cs

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

public class MaterialChanger {
    private GameObject gameObject;
    private Dictionary<MeshRenderer, Material> defaultMaterials = new Dictionary<MeshRenderer, Material>();

    public MaterialChanger(GameObject gameObject) {
        this.gameObject = gameObject;

        StoreDefaultMaterials();
    }

    private void StoreDefaultMaterials() {
        defaultMaterials.Clear();
        MeshRenderer[] meshRenderers = gameObject.GetComponentsInChildren<MeshRenderer>();
        foreach (MeshRenderer mr in meshRenderers) {
            defaultMaterials.Add(mr, mr.material);
        }
    }

    public void SetMaterialOnAllMeshRenderers(Material material) {
        foreach (MeshRenderer mr in defaultMaterials.Keys) {
            mr.material = material;
        }
    }

    public void RestoreDefaultMaterials() {
        foreach (MeshRenderer mr in defaultMaterials.Keys) {
            mr.material = defaultMaterials[mr];
        }
    }
}