Helper.cs

using System;
using System.IO;
using System.Linq;
using UnityEditor;
using UnityEngine;

[System.Serializable]
public struct NPrefabRef<T> : IDisposable
{
    public GameObject root;
    public T data;
    public string assetPath;
    public bool isNew;

    public void Dispose()
    {
#if UNITY_EDITOR
        if (root == null) return;
        if (isNew)
        {
            UnityEngine.Object.DestroyImmediate(root);
        }
        else
        {
            PrefabUtility.UnloadPrefabContents(root);
        }
#endif
    }
}

public class NPrefabService
{
    private static string NormalizePath(string path)
    {
        var pathComponents = path.Split('/').Where(i => !string.IsNullOrEmpty(i)).ToList();
        var partial = pathComponents.Count == 0 ? "" : pathComponents[0];
        for (var i = 1; i < pathComponents.Count; i++)
        {
            partial = Path.Combine(partial, pathComponents[i]);
        }

        return partial;
    }

    /// <summary>
    /// Return the full physical system path for the given asset path.
    /// </summary>
    public string PhysicalPath(string path)
    {
        var assetPath = NormalizePath(path);
        return Path.Combine(UnityEngine.Application.dataPath, assetPath);
    }

    public NPrefabRef<T> LoadPrefab<T>(string assetPath)
    {
        var physicalPath = PhysicalPath(assetPath) + ".prefab";
        Debug.Log(physicalPath);
        Debug.Log(File.Exists(physicalPath));

        GameObject instance = null;
        instance = PrefabUtility.LoadPrefabContents(physicalPath);
        Debug.Log($"Loaded: {instance}");

        var rtn = new NPrefabRef<T>()
        {
            root = instance,
            data = instance.GetComponent<T>(),
            assetPath = assetPath,
            isNew = false
        };

        if (rtn.data == null)
        {
            rtn.Dispose();
            throw new Exception($"No element of type {nameof(T)} on prefab at: {physicalPath}");
        }

        return rtn;
    }

    public void SavePrefab<T>(NPrefabRef<T> prefabRef)
    {
        var assetPath = PhysicalPath(prefabRef.assetPath) + ".prefab";
        PrefabUtility.SaveAsPrefabAssetAndConnect(prefabRef.root, assetPath, InteractionMode.AutomatedAction);
    }
}