そのフィールドをインスペクタから変更できなくする自作属性

NonEditableAttribute.cs

#if UNITY_EDITOR

using UnityEditor;
using UnityEngine;

namespace shigeno_EditorUtility
{
    public class NonEditableAttribute : PropertyAttribute
    {

    }

    [CustomPropertyDrawer(typeof(NonEditableAttribute))]
    public class NonEditableDrawer : PropertyDrawer
    {
        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        {
            NonEditableAttribute NonEditable = (NonEditableAttribute) attribute;
            
            EditorGUI.BeginDisabledGroup(true);
            
            EditorGUI.PropertyField(position, property, label);
            
            EditorGUI.EndDisabledGroup();
        }
    }

}

#endif