function Set-PowAsDefault
{
  [CmdletBinding()]
  Param
  (
    [Parameter(mandatory=$false,ValueFromPipeline=$false)]
    [Alias("Active")]
    [switch]
    [bool]$On
  )

  begin 
  {
    if ($On.IsPresent)
    {
      Write-Host "Call Powershell for .PS1 files."
    }
    else
    {
      Write-Host "Try to go back."
    }
  }

  Process 
  {
    # Text Menu
    [string]$TexteMenu = "Go inside PowerShell"

    # Text of the program to create
    [string] $TexteCommande = "%systemroot%\system32\WindowsPowerShell\v1.0\powershell.exe -Command ""&'%1'"""

    # Key to create
    [String] $clefAModifier = "HKLM:\SOFTWARE\Classes\Microsoft.PowerShellScript.1\Shell\Open\Command"

    try
    {
      $oldCmdKey = $null
      $oldCmdKey = Get-Item $clefAModifier -ErrorAction SilentlyContinue
      $oldCmdValue = $oldCmdKey.getvalue("")

      if ($oldCmdValue -ne $null)
      {
        if ($On.IsPresent)
        {
          $slxOldValue = $null
          $slxOldValue = Get-ItemProperty $clefAModifier -Name "slxOldValue" -ErrorAction SilentlyContinue
          if ($slxOldValue -eq $null)
          {
            New-ItemProperty $clefAModifier -Name "slxOldValue" -Value $oldCmdValue  -PropertyType "String" | Out-Null
            New-ItemProperty $clefAModifier -Name "(default)" -Value $TexteCommande  -PropertyType "ExpandString" | Out-Null
            Write-Host "Done !"
          }
          else
          {
            Write-Host "Already done !"          
          }

        }
        else
        {
          $slxOldValue = $null
          $slxOldValue = Get-ItemProperty $clefAModifier -Name "slxOldValue" -ErrorAction SilentlyContinue 
          if ($slxOldValue -ne $null)
          {
            New-ItemProperty $clefAModifier -Name "(default)" -Value $slxOldValue."slxOldValue"  -PropertyType "String" | Out-Null
            Remove-ItemProperty $clefAModifier -Name "slxOldValue" 
            Write-Host "Done !"
          }
          else
          {
            Write-Host "No former value !"          
          }
        }
      }
    }
    catch
    {
      $_.exception.message
    }
  }
  end {}
}

Set-PowAsDefault -On