Store a path to a resource instead of referencing the object

ResourcePathAttribute.cs

using UnityEngine;
using System;

public class ResourcePathAttribute : PropertyAttribute {
    public Type resourceType;

    public ResourcePathAttribute(Type t) {
        this.resourceType = t;
    }
}

ResourcePathPropertyDrawer.cs

using System;
using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer(typeof(ResourcePathAttribute))]
public class ResourcePathPropertyDrawer : PropertyDrawer {

    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {
        if (property.propertyType == SerializedPropertyType.String) {

            Type objType = ((ResourcePathAttribute)attribute).resourceType;
            UnityEngine.Object obj = null;

            if (property.stringValue != "") {
                obj = Resources.Load(property.stringValue, objType);
            }

            obj = EditorGUI.ObjectField(position, label, obj, objType, false);
            string assetPath = AssetDatabase.GetAssetPath(obj);
            if (assetPath != "") {
                string[] split = assetPath.Split(new string[]{ "Resources/" }, StringSplitOptions.RemoveEmptyEntries);
                string ext = System.IO.Path.GetExtension(assetPath);
                property.stringValue = split[split.Length - 1].Replace(ext, "");
            }
        }
    }
}