ボタンを操作できるようにラップしたもの。スクリプトを追加すれば[UI/Button]を呼び出したのと同等の処理を行う。

ButtonTextCustomer

using UnityEngine;
using UnityEngine.UI;
using System.Reflection;

#if UNITY_EDITOR
using UnityEditor;
using UnityEditor.UI;
using UnityEditor.SceneManagement;
#endif

public class ButtonTextCustomer : Button, IControlText
{
    [SerializeField] Text _text;
    public void ChangeTextColor(Color color) => _text.color = color;


#if UNITY_EDITOR
    [CustomEditor(typeof(ButtonTextCustomer))]
    class ButtonTextCustomerCustom : ButtonEditor
    {
        ButtonTextCustomer _handle;
        protected override void OnEnable()
        {
            base.OnEnable();

            _handle = target as ButtonTextCustomer;
            if (!_handle._text)
            {
                var text = _handle.GetComponentInChildren<Text>(true);
                if (!text)
                {
                    // UnityEditor.EditorApplication.ExecuteMenuItemWithTemporaryContext(string menuItemPath, UnityEngine.Object[] objects) を呼び出す
                    var flag = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
                    var editorAppType = typeof(EditorApplication);
                    var uiMenuItemMethod = editorAppType.GetMethod("ExecuteMenuItemWithTemporaryContext", flag);
                    uiMenuItemMethod.Invoke(null, new object[] { "GameObject/UI/Text", new Object[] { _handle.gameObject } });

                    // 上記実行後に生成されたTextへフォーカスが移るので、それを取得する
                    text = Selection.activeTransform.GetComponent<Text>();
                    Selection.activeTransform = Selection.activeTransform.parent;
                }
                _handle._text = text;
                EditorSceneManager.MarkSceneDirty(UnityEngine.SceneManagement.SceneManager.GetActiveScene());
            }
        }

        public override void OnInspectorGUI()
        {
            _handle._text = (Text)EditorGUILayout.ObjectField("Text", _handle._text, typeof(Text), true);
            base.OnInspectorGUI();
        }
    }
#endif
}

interface IControlText
{
    void ChangeTextColor(Color color);
}