To get this script to work in 2011 and later, you need to do this to find the Blinn shaders:

// Get a collection of all Blinn nodes
var sProgID = "Softimage.material-blinn.1.0" 
var oShaderDef = Application.GetShaderDef( sProgID ) ;  

var oBlinnCollection =  oShaderDef.ShaderInstances ;  
if (debug) LogMessage( "Found " + oBlinnCollection.Count + " Blinn shaders" );

The rest of the script can stay the same.
Note: I split the script into two parts below, for the purposes of this blog post. Just combine them to get the full script.

Here’s a script that shows how to replace every Blinn shader in a scene with a Phong shader.
There’s other ways to do it, but I used the connection stack.

var debug = 0;

// Class ID of the Blinn shader in XSI
var sClassID = "{8FAC63AC-E392-11D1-804C-00A0C906835D}";
SetValue("preferences.scripting.cmdlog", false, null);

// Get a collection of all Blinn nodes
var oBlinnCollection = FindObjects( null, sClassID );
if (debug) LogMessage( "Found " + oBlinnCollection.Count + " Blinn shaders" );

// Loop over the Blinn collection and replace all Blinn nodes with Phongs
var s = new Date();
oEnum = new Enumerator( oBlinnCollection ) ;
for (;!oEnum.atEnd();oEnum.moveNext() )
{
	var oBlinn = oEnum.item() ;

	// try catch will skip over any TransientObjectContainer.Blinn shaders we find
	try
	{
		var oMaterial = oBlinn.Owners(0);
	}
	catch(e)
	{
		LogMessage( "Skipping " + oBlinn );
		continue;
	}
	LogMessage( "Replacing " + oBlinn );
	blinn2phong( oMaterial, oBlinn );
}
var e = new Date();
LogMessage( "Finished replacing Blinn shaders. Elapsed time: " + (e-s)/1000 + "s" );



function blinn2phong( oMaterial, oBlinn )
{
	// Create a new Phong node
	var oPhong = CreateShaderFromPreset("$XSI_DSPRESETS\\Shaders\\Material\\Phong.Preset", oMaterial, null);

	// Get the node connections from the ConnectionStack
	// And then insert the Phong node

	var oDR = XSIUtils.DataRepository ;
	var strOpInfo = oDR.GetConnectionStackInfo( oBlinn );

	var oTopNode = ParseXML( strOpInfo ) ;
	var oConnections = oTopNode.childNodes ;

	if ( oConnections.length == 0 )
	{
		LogMessage( "Cannot replace the Blinn node " + oBlinn + " .It has no connections." );
	}
	else
	{

		for ( var i = 0 ; i < oConnections.length ; i++ )
		{
			var oConnection = oConnections(i) ;
							
			strtype = SafeGetNodeValue( oConnection, "type", "Unknown" ) ;
			strobj = SafeGetNodeValue( oConnection, "object", "Not Connected" ) ; 
			localparam = SafeGetNodeValue( oConnection, "localparameter", "&nbsp;" ) ;  
			destparam = SafeGetNodeValue( oConnection, "remoteparameter", "&nbsp;" ) ;  				
			
			if ( strtype == "in" )
			{
				var oParam = oPhong.Parameters( localparam );
				if ( oParam == null )
				{
					LogMessage( "Cannot connect " + strobj + " to Phong." + localparam + ". That parameter does not exist.", siWarning );
				}
				else
				{
					//SIConnectShaderToCnxPoint("Sources.Materials.Proteus_Body_MatLib_Proteus.MAT_Brass11.Image5", oPhong + ".ambient", false);
					SIConnectShaderToCnxPoint( strobj, oParam );
					if( debug ) LogMessage( "IN: " + strobj + ", " + oParam );
				}
			}
			if ( strtype == "out" )
			{
				var oTarget = Dictionary.GetObject( strobj );
				var oParam = oTarget.Parameters( destparam );
				//SIConnectShaderToCnxPoint("Sources.Materials.Proteus_Body_MatLib_Proteus.MAT_Brass11.Phong1", "Sources.Materials.Proteus_Body_MatLib_Proteus.MAT_Brass11.Mix_2colors.base_color", false);
				SIConnectShaderToCnxPoint( oPhong, oParam );
				if( debug ) LogMessage( "OUT: " + oPhong + ", " + oParam );
			}
		}	
	}
}

The bling2phong() function is based on the code that builds this HTML page in the SDK Explorer:

Notice how the Connection Stack Details give you everything you need to replace a Blinn node with some other node in the render tree:

See below the cut for the code for the helper functions ParseXML() and SafeGetNodeValue().

//----------------------------------------
// Helpers
//----------------------------------------


// Helper function to load the XML data using the Microsoft
// implementation of the DOM (see msdn.microsoft.com for documentation)
function ParseXML( strXML )
{
	var oXMLParser = new ActiveXObject("Microsoft.XMLDOM") 
	oXMLParser.async = false	
	oXMLParser.loadXML( strXML ) ;

	if (oXMLParser.parseError.errorCode != 0) 
	{
		logmessage( "Invalid XML " + oXMLParser.parseError.reason , siError ) ;	
		return null ;
	}

	// the xsi_file node
	// If this is NULL we must have failed to load the XML
	var oTopNode = oXMLParser.documentElement ;

	return oTopNode ;
}

// SafeGetNodeValue
//
// in_parentnode - XML DOM node
// in_nodename - name of a nested node to query
// in_default - value to return if nested node not found
//
// Example: If in_parent node points to this XML: <item><info>4</info><other></other></item>
// then SafeGetNodeValue( node, "info", 0 ) ; returns "4".
// and SafeGetNodeValue( node, "bogus", "not found" ) ; returns "not found".
function SafeGetNodeValue( in_parentnode, in_nodename, in_default )
{
	strInfo = in_default ;

	try
	{
		oNode = in_parentnode.selectSingleNode( in_nodename ) ;
		if ( oNode != null )
		{
			// Note: the property name is case sensitive, "Text" does not work
			strInfo = oNode.text ;  
		}
	}
	catch( e )
	{
	}
	return strInfo ;	
}