DSplineUtilMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Splines;
using UnityEditor;

public static class DSplineUtilMenu
{
    [MenuItem("Spline/FreezeTransform")]
    public static void FreezeTransform()
    {
        var o = Selection.activeGameObject;
        if (o)
        {
            var splineContainer = o.GetComponent<SplineContainer>();
            if (splineContainer)
            {
                var mat = o.transform.localToWorldMatrix;
                foreach(var spline in splineContainer.Splines)
                {
                    for(int idKnot =0;idKnot<spline.Count;++idKnot)
                    {
                        var k = spline[idKnot];
                        var newKnot = k.Transform(mat);
                        spline[idKnot] = newKnot;
                    }
                }
                o.transform.localPosition = Vector3.zero;
                o.transform.localRotation = Quaternion.identity;
                o.transform.localScale = Vector3.one;
            }
        }
    }
}