Convert renderings from Sitecore 8 to 9+ version

SitecoreMigrateRenderings8to10.ps1

# specify your path here. It is most likely be page templates and page content
$startPath = "/sitecore/content"
Get-ChildItem -Path $startPath -Recurse | ForEach-Object {
    $item = $_;    
    Get-Rendering -Item $_ -FinalLayout | ForEach-Object {
        $rendering = $_;
        $matches = [regex]::Matches($_.Placeholder,'(?<guid>_[\d\w]{8}\-(?:[\d\w]{4}\-){3}[\d\w]{12})(?<seed>_?\d?)')
        if ($matches.Success) {
            Write-Host "Match found in item - [$($item.Paths.FullPath)]"
            Write-Host "Old Placeholder - [$($rendering.Placeholder)]"
            $newPlaceholder = $rendering.Placeholder
            $matches | ForEach-Object {
                $match = $_
                $renderingId = $match.Value
                if (!([string]::IsNullOrEmpty($match.Groups["seed"])))
                {
                    $seedSuffix = $match.Groups["seed"].ToString()
                    $seedValue = $seedSuffix.Trim("_")
                    # trim seed suffix off end 
                    $unsuffixedRenderingId = $renderingId.ToString().TrimEnd($seedSuffix)
                    # add seed value to end 
                    $newPlaceholder = $newPlaceholder.Replace($renderingId, "{$($unsuffixedRenderingId.ToUpper())}-$seedValue")
                }
                else
                {
                    $newPlaceholder = $newPlaceholder.Replace($renderingId, "{$($renderingId.ToUpper())}-0")
                }
            }
            $newPlaceholder = $newPlaceholder.Replace('{_', "-{")
            Write-Host "New Placeholder - [$($newPlaceholder)]"
            # comment following 2 lines if you don't want to do replacement, but want to have log of upcoming placeholder changes
            $rendering.Placeholder = $newPlaceholder
            Set-Rendering -Item $item -Instance $rendering -FinalLayout
        }
    }
}