I hope use API method

the a.sldprt replace b.sldprt in Drawing of a.slddrw

In Drawing of a.slddrw, display b.sldprt.

Record Macro,But don't repalce sldprt.

' ******************************************************************************
' C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\swx3712\Macro1.swb - macro recorded on 11/19/12 by Administrator
' ******************************************************************************
Dim swApp As Object
Dim Part As Object
Dim SelMgr As Object
Dim boolstatus As Boolean
Dim longstatus As Long, longwarnings As Long
Dim Feature As Object
Sub main()

   Set swApp = Application.SldWorks

   Set Part = swApp.OpenDoc6("D:\Backup\我的文档\DrawingSld\a.SLDDRW", 3, 0, "", longstatus, longwarnings)
   Set Part = swApp.ActivateDoc2("a - 图纸1", False, longstatus)
End Sub