Cannot find registry path running a powershell script as a custom action

I have a PowerShell script where I am reading and editing registry.

I tried running it manually, calling it from command line, converting it to an .exe with ps2exe, and for all of those scenarios it works as intended. However, when I package it with my installer (using MS Visual Studio Installer Projects) and try running it as Custom Actions/Commit/script.exe, it suddenly cannot find the registry keys.

Here's a snippet of my script.

## initializing new variables
$req_path = Get-Item -Path "HKCU:\SOFTWARE\Microsoft\Office\16.0\Excel\Options" |
  Select-Object -ExpandProperty Property
echo $req_path

ERROR: Get-Item : Cannot find path
'HKCU:\SOFTWARE\Microsoft\Office\16.0\Excel\Options' because it doesnot exist.

I have also tried this variation to no avail:

$req_path = Get-Item -Path Registry::HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Excel\Options |
  Select-Object -ExpandProperty Property

Since this is part of the installer, it runs as admin, so privileges are not the culprit.

So, How can I access the registry keys when running a PowerShell script as a custom action?

Some additional info.:

• [Environment]::Is64BitProcess returns True
• WhoAmI returns nt authority\system

^{Considering that I am not an expert in powershell, there is a great chance that there is a better way or at least my implementation is not the most efficient one, but I found a way.}

## HKCU is not accessible when running the script from nt\ authority system
## Hence, accessing the HKU/SID for the current user
## finding current user's SID
## list of profiles
$profileIP = 
(Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList\*") | 
Select-Object ProfileImagePath
$profileIP = $profileIP.ProfileImagePath

## list of SIDs
$SIDs = 
(Get-ChildItem -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList\") | 
Select-Object Name 
$SIDs = (Split-Path $SIDs -Leaf).Trim("{}")

## finding the SID for the current user
$sid_index = 0

foreach ($entry in $profileIP) {
    if ($entry.ToString().ToUpper().Contains($env:USERNAME.ToUpper())){break}
    $sid_index += 1
}

$CU_SID = $SIDs[$sid_index]

## initiating HKU for this instance of powershell
New-PSDrive -PSProvider Registry -Name HKU -Root HKEY_USERS

## Get items under SOFTWARE\Microsoft\Office\16.0\Excel\Options
$req_ref = -join @("HKU:\",$CU_SID,"\SOFTWARE\Microsoft\Office\16.0\Excel\Options")
$req_path = Get-Item -Path $req_ref |
  Select-Object -ExpandProperty Property