Remove unsupported content from bacpac/dacpac files, to allow them to be loaded in older versions of SQL

Convert-ToSimpleBacPac.ps1

function New-TemporaryDirectory {
    [CmdletBinding()]
    Param ()
    Process {
        [string]$path = Join-Path -Path ([System.IO.Path]::GetTempPath()) -ChildPath ([System.Guid]::NewGuid())
        New-Item -ItemType Directory -Path $path
    }
}
function Update-BacPacChecksum {
    [CmdletBinding()]
    Param (
        #improve: allow a compressed bacpac to be sent & have this update the internal file (for now just written to support the below rather than to fix any corrupted bacpac's checksum
        [Parameter(Mandatory = $true)]
        [string]$ExtractedBacPacPath
    )
    Process {
        [string]$modelPath  = Join-Path -Path $tempPath -ChildPath 'model.xml'
        [string]$originPath = Join-Path -Path $tempPath -ChildPath 'Origin.xml'
        [System.Security.Cryptography.HashAlgorithm]$hasher = [System.Security.Cryptography.HashAlgorithm]::Create('System.Security.Cryptography.SHA256CryptoServiceProvider')
        [System.IO.FileStream]$fileStream = [System.IO.FileStream]::new($modelPath, [System.IO.FileMode]::Open)
        [byte[]]$hash = $hasher.ComputeHash($fileStream)
        $fileStream.Close()
        [string]$hashString = ($hash | %{$_.ToString('X2')}) -join ''
        [xml]$origin = (Get-Content -Path $originPath -Raw)
        [System.Xml.XmlNamespaceManager] $xnm = [System.Xml.XmlNamespaceManager]::new($origin.NameTable);
        $xnm.AddNamespace('dac', 'http://schemas.microsoft.com/sqlserver/dac/Serialization/2012/02')
        $origin.SelectSingleNode('/dac:DacOrigin/dac:Checksums/dac:Checksum[@Uri="/model.xml"]/text()', $xnm).Value = $hashString
        $origin.Save($originPath)
    }
}
function Convert-ToSimpleBacPac {
    [CmdletBinding()]
    Param (
        [Parameter(Mandatory = $true)]
        [string]$SourceFilename
        ,
        [switch]$RemoveColumnStoreIndex
        ,
        [switch]$RemoveFullTextIndex
        ,
        [int]$MaxColumnsPerIndex = ([int]::MaxValue-1) #removes any indexes which have too many columns to exist (doesn't just truncate, since that would impact unique indexes / I couldn't be bothered to get clever)
    )
    Process {
        [string]$tempPath = (New-TemporaryDirectory).Fullname
        [string]$modelPath = Join-Path -Path $tempPath -ChildPath 'model.xml'
        Expand-Archive -Path $SourceFilename -DestinationPath $tempPath #in theory we could just grab the model from the bacpac, then overwrite that file; but for now going for speed of dev over speed of performance...
        [xml]$model = (Get-Content -Path $modelPath -Raw)
        [System.Xml.XmlNamespaceManager] $xnm = [System.Xml.XmlNamespaceManager]::new($model.NameTable);
        $xnm.AddNamespace('dac', 'http://schemas.microsoft.com/sqlserver/dac/Serialization/2012/02')
        
        if ($RemoveColumnStoreIndex.IsPresent) {
            $model.SelectNodes("/dac:DataSchemaModel/dac:Model/dac:Element[@Type = 'SqlColumnStoreIndex']",$xnm) | %{$_.ParentNode.RemoveChild($_) | Out-Null}
        }

        if ($RemoveFullTextIndex.IsPresent) {
            $model.SelectNodes("/dac:DataSchemaModel/dac:Model/dac:Element[@Type = 'SqlFullTextIndex']",$xnm) | %{$_.ParentNode.RemoveChild($_) | Out-Null}
        }

        $MaxColumnsPerIndex = $MaxColumnsPerIndex+1
        $model.SelectNodes("/dac:DataSchemaModel/dac:Model/dac:Element[@Type = 'SqlPrimaryKeyConstraint' or @Type = 'SqlIndex' or @Type = 'SqlUniqueConstraint' or @Type = 'SqlFullTextIndex'][./dac:Relationship/dac:Entry[ $MaxColumnsPerIndex ]]",$xnm) | %{$_.ParentNode.RemoveChild($_) | Out-Null}

        <#NVENTQUALITYORDERCREATIONPOLICYSTAGING
        Other values are available
        $model.SelectNodes('/dac:DataSchemaModel/dac:Model/dac:Element/@Type',$xnm) | select -ExpandProperty value -Unique
            SqlCheckConstraint
            SqlDatabaseOptions
            SqlDefaultConstraint
            SqlPrimaryKeyConstraint
            SqlRoleMembership
            SqlSchema
            SqlTable
            SqlIndex
            SqlFullTextIndex
            SqlUniqueConstraint
            SqlUser
            SqlLogin
            SqlFullTextCatalog
            SqlTableType
            SqlView
            SqlProcedure
            SqlInlineTableValuedFunction
            SqlMultiStatementTableValuedFunction
            SqlScalarFunction
            SqlRole
            SqlDmlTrigger
            SqlColumnStoreIndex
            SqlForeignKeyConstraint
            SqlSequence
            SqlPermissionStatement
        #>
        $model.Save($modelPath)
        Update-BacPacChecksum -ExtractedBacPacPath $tempPath
        Compress-Archive -Path $tempPath -DestinationPath "$SourceFilename.zip" 
        Rename-Item -Path "$SourceFilename.zip" -NewName $SourceFilename
        Remove-Item -Path $tempPath
    }
}
#Convert-ToSimpleBacPac -SourceFilename 'c:\temp\mybacpac.bacpac' -RemoveColumnStoreIndex -MaxColumnsPerIndex 16 #example usage

Caught out by the checksum :/
Thankfully there is a fix:

• https://blogs.msdn.microsoft.com/azuredev/2016/09/25/sql-azure-tip-failures-importing-bacpac/
• https://blogs.msdn.microsoft.com/azuresqldbsupport/2017/08/16/editing-a-bacpac-file/

Note: Compress-Archive and Expand-Archive could be replaced by the 7zip module's equivelant (Compress-7Zip -Path $sourcePath -ArchiveFileName $archivePath -Format Zip). See https://www.powershellgallery.com/packages/7Zip4Powershell. This would give better performance as well as making potential out-of-memory issues less likely.