Updating XML elements & attributes within stored procedure

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C#

SQL-Server

SQL-Server-2008

I need some help here! many thanks to anyone that attempts.

One of the args of this procedure (@NextSlot) is an XML datatype. How do I edit/update/add-to its nodes (attributes and elements) before saving it to dbase.

ALTER PROCEDURE dbo.GetXmlData
(
	@NextSlot XML OUTPUT,
	@RowID BIGINT
)	
AS
	SET NOCOUNT ON 

	DECLARE @TransXEl XML, @XmlHandle INT, @CurrentStatus NVARCHAR(20)

	SET @TransXEl = (SELECT ContextCol FROM XElTab WHERE RowID = @RowID)
	
		EXEC sp_xml_preparedocument @XmlHandle OUTPUT, @TransXEl;

		SET @CurrentStatus =  (SELECT VariationStatus FROM OPENXML (@XmlHandle, '/PayPattern', 2)
		WITH (VariationStatus VARCHAR(20) '@VariationStatus'))

		IF(@CurrentStatus = 'Vacant')
	-- HOW DO I  UPDATE ELEMENT @CurrentStatus IN @NextSlot
		--AS IN @NextSlot.Element('CurrentStatus').Value = Vacant

	-- OR ADD A NEW ATTRIBUTE TO @TransXEl
    		-- AS IN @TransXEl.Add(new XAttribute('NewAttrib', 'NewValue')

	---OR UPDATE USING OPENXML HANDLE
		-- AS IN UPDATE  OPENXML (@XmlHandle, '/PayPattern', 2) SET 
--'@VariationStatus' = 'ALLOCATED')

believe it or not, too much is at stake for this and many hands are waiting idle for the impasse to be broken! please help!