Edit the metadata header of a VMDK file

Edit-VMDKHeader.ps1

Set-StrictMode -Version Latest

function Edit-VMDKHeader {
    <# .SYNOPSIS
    Edit the metadata header of a VMDK file #>
    [CmdletBinding(SupportsShouldProcess, ConfirmImpact = 'High')]
    Param(
        # The VMDK file to edit
        [Parameter(Mandatory)]
        [string]$VMDKFile
    )

    $buffer = [byte[]]::new(1024)
    $tmpFile = [IO.Path]::Combine([IO.Path]::GetTempPath(), [IO.Path]::GetTempFileName())

    $vmdkStream = [IO.File]::Open($VMDKFile, [IO.FileMode]::Open, [IO.FileAccess]::ReadWrite)
    $vmdkStream.Position = 512
    [void]$vmdkStream.Read($buffer, 0, 1024)

    Write-Output 'Dumping VMDK header metadata to:' $tmpFile
    $tmpStream = [IO.File]::OpenWrite($tmpFile)
    $tmpStream.Write($buffer, 0, 1024)
    $tmpStream.Dispose()

    Write-Output 'Make necessary changes, then save and close the editor.'
    (Start-Process notepad.exe -ArgumentList $tmpFile -PassThru -Wait).WaitForExit()

    $tmpStream = [IO.File]::OpenRead($tmpFile)
    [void]$tmpStream.Read($buffer, 0, 1024)
    $tmpStream.Dispose()
    Remove-Item $tmpFile

    if ($PSCmdlet.ShouldProcess($VMDKFile, 'Overwrite VMDK header metadata')) {
        Write-Output 'Overwriting VMDK header metadata.'
        $vmdkStream.Position = 512
        $vmdkStream.Write($buffer, 0, 1024)
    }
    $vmdkStream.Dispose()
}

A function implementing the commands from this SO answer to edit VMDK metadata.
This was necessary in order to solve this problem when converting VMDK files to VHDX.

Updated version available in my HelperFunctions module.