Hi Gérard,

for encluding bookmarks, like [some text]:

Public Sub NewText(sBkm As String, sTmp As String)
Dim rTmp As Range
With ActiveDocument.Bookmarks
  If .Exists(sBkm) Then
     Set rTmp = .Item(sBkm).Range
     rTmp.Text = sTmp
     .Add Name:=sBkm, Range:=rTmp
  End If
End With
End Sub

Sub test4001()
  NewText "Mark01", "2nd Text"
End Sub

The bookmark gets lost and has to be recreated.

With excluding bookmarks, like ][,
it's not a problem anyway.

There is a nice tool from Greg Maxey:
http://gregmaxey.mvps.org/Bookmark_Tool.htm

See the article "Inserting text at a bookmark without deleting the bookmark"
at:

http://www.word.mvps.org/FAQs/MacrosVBA/InsertingTextAtBookmark.htm