Template task detail modify project server using Microsoft.Office.Interop.MSProject.Project

Hello Everyone !!!

I want to modify the tempate task custom field and save the template again using Microsoft.Office.Interop.MSProject.Project

I have written below code

 For Each tsk As Microsoft.Office.Interop.MSProject.Task In PrjWsApp.ActiveProject.Tasks

                If Not tsk Is Nothing Then
                        tsk.Name = "test task update"
                End If
            Next tsk

PrjWsApp.DisplayAlerts = False
            PrjWsApp.FileSave()
            PrjWsApp.FileCloseEx(Microsoft.Office.Interop.MSProject.PjSaveType.pjSave, , True)
            PrjWsApp.DisplayAlerts = True

but it is not updating the template. Please suggest how to update the template and save it