ToNumbering.cs

using System.Text.RegularExpressions;
using UnityEditor;
using UnityEngine;

public class ToNumbering : EditorWindow
{

    private string baseName = "";

    // Add menu item named "My Window" to the Window menu
    [MenuItem("Tools/ToNumbering")]
    public static void ShowWindow()
    {
        //Show existing window instance. If one doesn't exist, make one.
        EditorWindow.GetWindow(typeof(ToNumbering));
    }

    void OnGUI()
    {
        GUILayout.Label("What is base name?", EditorStyles.boldLabel);
        baseName = EditorGUILayout.TextField("Base Name", baseName);
        if (GUILayout.Button("Excute"))
        {
            Ordering(baseName);
            Debug.Log("Renamed.");
        }

    }

    void Ordering(string baseName)
    {
        Undo.RecordObjects(Selection.objects, "modify name");

        int count = Selection.objects.Length;
        int d = count.ToString().Length;

        for (int i = 0; i < count; i++)
        {
            string newname = Regex.Replace(baseName, @"_(\d)+$", "");
            Selection.objects[i].name = newname + "_" + i.ToString().PadLeft(d, '0');
        }
    }
}