Installing MSI several times

InstallMsi.ps1

param (
   [Parameter(Mandatory=$false)][string]$Instance
)
[string]$DefaultInstance = "MyProduct_MSI"
if ($Instance) {
 Write-Host "Copying installer to $($Instance).msi"
 Copy-Item "MyProduct_MSI.msi" "$($Instance).msi"
 $md5 = new-object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
 $utf8 = new-object -TypeName System.Text.UTF8Encoding
 $hash = (new-object -TypeName System.Guid -ArgumentList @(,$md5.ComputeHash($utf8.GetBytes($Instance)))).ToString().ToUpper()
  Write-Host "Product code: $($hash)"
 Write-Host "Injecting product code into $($Instance).msi"
 Invoke-Expression -Command:"cscript wirunsql.vbs $($Instance).msi ""UPDATE Property SET Value='{$($hash)}' WHERE Property='ProductCode'"""
 Invoke-Expression -Command:"cscript wirunsql.vbs $($Instance).msi ""UPDATE Property SET Value='MyProduct ($($Instance))' WHERE Property='ProductName'"""
 Invoke-Expression -Command:"cscript wirunsql.vbs $($Instance).msi ""UPDATE Property SET Value='{$($hash)}' WHERE Property='UpgradeCode'"""
 Invoke-Expression -Command:"cscript wisuminf.vbs $($Instance).msi Revision='{$($hash)}'"
}
else {
 $Instance = $DefaultInstance
}
Write-Host "Launching installer package..."
Invoke-Expression -Command:"msiexec /i $($Instance).msi"