How to freeze rotation and transform from HMD's children

Hello everybody,

I'm currently working on a game overlay project.
I've a VR aircraft game using SteamVR to provide its VR experience. I would like to create an custom cockpit Overlay to interact with. I use the BenotterOVRlay (link). This overlay doesn't allow me to set my project as XR/VR but I can get my project to work properly.

Unfortunetaly, when I launch my aircraft game, it transform my HMD position and rotation. And it result in a non centered overlay regarding to the aircraft cockpit.
So I set all my overlays as HMD children in order to get their positions set relative to the HMD when I start, and I tried to freeze the rotation and transform of all my cockpit's overlays objects using this code :

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class RotFreeze : MonoBehaviour {
6.     Quaternion rotation;
7.     Vector3 position;
8.     // Use this for initialization
9.     void Start () {
10.      
11.         rotation = transform.rotation;
12.         position = transform.position;
13.     }
14.  
15.     // Update is called once per frame
16.     void Update () {
17.         transform.rotation = rotation;
18.         transform.position = position;
19.     }
20. }

But this doesn't seem to work, overlays are statics but they're not centered.
Can somebody give me advise about this ?

Thanks