Unity5のエディタ拡張？について

例えば、以下のようなクラスを用意してGameObjectにアタッチ

using UnityEditor;
using UnityEngine;

public class editorTest : MonoBehaviour {

    public Vector3 position
    {
        get
        {
            return transform.position;
        }
        set
        {
            transform.position = value;
        }
    }
    public Vector3 scale
    {
        get
        {
            return transform.localScale;
        }
        set
        {
            transform.localScale = value;
        }
    }

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {

    }
}

Editor側では、OnInspectorGUIでflg変数を用意してGUILayout.Toggleで制御し、flgの値によりEditorGUILayout.xxxxの実行を制御すればできるかと思います。

[CustomEditor(typeof(editorTest))]
[CanEditMultipleObjects]
public class PosiitonScaleEditor : Editor
{
    bool flg = false;

    public override void OnInspectorGUI()
    {
        serializedObject.Update();
        var test = target as editorTest;
        flg = GUILayout.Toggle(flg, "Position & Scale");
        if (flg)
        {
            test.position = EditorGUILayout.Vector3Field("Position", test.position);
            test.scale = EditorGUILayout.Vector3Field("Scale", test.scale);
        }
        serializedObject.ApplyModifiedProperties();
    }
}