ReadWriteModelPostprocessor.cs

using UnityEditor;
using UnityEngine;

public class ReadWriteModelPostprocessor : AssetPostprocessor
{
    void OnPreprocessModel()
    {
        Debug.Log("Setting Read/Write permission automatically... Delete this script if this is not intended.");
        ModelImporter modelImporter = assetImporter as ModelImporter;
        modelImporter.isReadable = true;
    }
}