.cs

[HarmonyPatch(typeof(CarScreenLogic), "OnPlayerEventCarInstantiate")]
internal class Tmp2
{
    static void Postfix(CarScreenLogic __instance)
    {
        var url = "https://i.imgur.com/jFR3Vat.jpg";
        var newTexture = new Texture2D(1, 1);
        using (WWW www = new WWW(url))
        {
            while (!www.isDone) {} // bad
            www.LoadImageIntoTexture(newTexture);
        }

        Renderer[] componentsInChildren = Traverse.Create(__instance).Field("carTrans_").GetValue<Transform>().GetComponentsInChildren<Renderer>();
        foreach (Renderer renderer in componentsInChildren)
        {
            Material[] materials = renderer.materials;
            foreach (Material material in materials)
            {
                if (material.HasProperty("_CarScreenTex"))
                {
                    material.SetTexture("_CarScreenTex", newTexture);
                }
            }
        }
    }
}