Use Set-ItemTemplate to fix an item with a missing template

Question

Is there way to use Set-ItemTemplate to fix an item with a broken (deleted) template?

I'm trying the following script but get a null reference error

$item = Get-Item -Path master: -Query "/sitecore/content/MyProject/Commerce Websites/MyWebsite/Data/Sliders/Option Folder"
$sliderDataFolderTemplate = Get-Item -Path master: -ID "{551BBAE9-84F4-4393-BB96-5BB410203B86}"

Set-ItemTemplate -ID $item.ID -TemplateItem $sliderDataFolderTemplate

which results in:

Set-ItemTemplate : Object reference not set to an instance of an object.
At line:4 char:1
+ Set-ItemTemplate -ID $item.ID -TemplateItem $sliderDataFolderTemplate
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Set-ItemTemplate], NullReferenceException
    + FullyQualifiedErrorId : System.NullReferenceException,Cognifide.PowerShell.Commandlets.Data.SetItemTemplateCommand

I tried wrapping Set-ItemTemplate with an EventDisabler context but that did not fix the problem.

New-UsingBlock (New-Object Sitecore.Data.Events.EventDisabler) {     
  Set-ItemTemplate -ID $item.ID -TemplateItem $sliderDataFolderTemplate
}

Answer 1

Not the nicest way but you may try to call TemplateManager.ChangeTemplate method:

$newTemplateIdString = "{76036F5E-CBCE-46D1-AF0A-4143F9B557AA}";
$itemIdString = "{A3FEC1DD-813C-44BD-9A37-66F0FADFD32F}"

$db = [Sitecore.Data.Database]::GetDatabase("master");
$templateId = [Sitecore.Data.ID]::Parse($newTemplateIdString)
$template = [Sitecore.Data.Managers.TemplateManager]::GetTemplate($templateId, $db)
$item = $db.GetItem($itemIdString)

$parameters = @{
    TypeName = 'Sitecore.Data.Templates.TemplateChangeList'
    ArgumentList = ($template, $template)
}

$templateChangeList = New-Object @parameters

[Sitecore.Data.Managers.TemplateManager]::ChangeTemplate($item, $templateChangeList)