A Question about how to programmatically modify XData Block

Here is an example code to modify or create a production XData block, i guess you can adapt to you needs :

ClassMethod CreateProduction(
	package As %String = "test",
	name As %String = "AutoCreatedProduction",
	xdata As %CharacterStream) As %Status
{
  #Dim produtionClassName As %String = package _ "." _ name
  If ('$ZName(produtionClassName, 4))
  {
  Return $System.Status.Error(5001, "Invalid Production package or name.")
  }
  #Dim productionDefinition As %Dictionary.ClassDefinition
  // Check if the production already exists
  If (##class(%Dictionary.ClassDefinition).%ExistsId(produtionClassName))
  {
	// Open the production
	set productionDefinition = ##class(%Dictionary.ClassDefinition).%OpenId(produtionClassName)
  }
  Else
  {
	// Create the production definition
    set productionDefinition = ##Class(%Dictionary.ClassDefinition).%New()
  }
  //
  Set productionDefinition.Name         = produtionClassName
  Set productionDefinition.Super        = "Ens.Production"
  Set productionDefinition.ClassVersion = 25
  //
  // Check if the XData Definition already exists
  If (##Class(%Dictionary.XDataDefinition).%ExistsId(produtionClassName_"||ProductionDefinition"))
  {
	// delete the XData Definition
	$$$ThrowOnError(##Class(%Dictionary.XDataDefinition).%DeleteId(produtionClassName_"||ProductionDefinition"))
  }
  #Dim xdataDefinition As %Dictionary.XDataDefinition = ##Class(%Dictionary.XDataDefinition).%New()
  //
  Set xdataDefinition.Name = "ProductionDefinition"
  //
  Do xdataDefinition.Data.CopyFrom(xdata)
  //
  // Insert XData Definition into Production Definition
  Do productionDefinition.XDatas.Insert(xdataDefinition)
  //
  #Dim statusCode As %Status = productionDefinition.%Save()
  //
  If ($System.Status.IsError(statusCode))
  {
  Return statusCode
  }
  // Compile the production class
  return $System.OBJ.Compile(produtionClassName,"k-d")
}

Not so much magic in it, if you already know how to read it, the content of XData is just a Stream, which can be used both ways. Just Write to it, and %Save it. And you will probably need to compile the class

Class Demo.Test
{

XData OpenAPI [ MimeType = application/json ]
{
}

ClassMethod Update()
{
    set xdata = ##class(%Dictionary.XDataDefinition).IDKEYOpen($ClassName(), "OpenAPI")
    do xdata.Data.Write("{}")
    do xdata.%Save()
}

}

In VSCode, the content of XData will not appear after that, because it happened on the server, and VSCode will not see the changes, you'll need to export it manually