How can we redifine a block in the same manner as we do manually with the command "insert blockname=".

I tried this:
Dwg=Activedocument
InsPt=Library.CreatePoint(0, 0, 0)
DwgName = "C:\BlockTest.dwg"
Dwg.ModelSpace.InsertBlock InsPt, DwgName

If the block with name DwgName (without the path) allready exists it's not redfined.

However, this works:
(blk=existing block reference)
RunCommand "insert " & blk.Name & "=" & blk.Name
RunCommand "0,0"
RunCommand "1"
RunCommand "1"
RunCommand "0"
Now the block is redifned, but it's not very elegant....

Any ideas?