The following works for Ref field updating and should give you a leg up.
Private Sub RefFieldUpdateAllStory()
'   Written by Charles Kyle Kenyon 15 November 2001
'   repaired by Jezebel
'   All Story Field Updater - Ref fields
   Dim oField As Field
   Dim oStory As Range
'
   For Each oStory In ActiveDocument.StoryRanges
   ' This goes into headers and footers as well as the regular document
       Do
           For Each oField In oStory.Fields
               If oField.Type = wdFieldRef Then
                   oField.Update
               End If
           Next oField
           Set oStory = oStory.Next
       Loop Until oStory Is Nothing
   Next oStory
End Sub

I haven't tested this yet:

Sub MergeFieldLockAllStory()
'   Written by Charles Kyle Kenyon 1 April 2005
'
'   All Story Field Locker - Merge fields
   Dim oField As Field
   Dim oStory As Range
'    On Error Resume Next
   For Each oStory In ActiveDocument.StoryRanges
   ' This goes into headers and footers as well as the regular document
       Do
           For Each oField In oStory.Fields
               If oField.Type = wdFieldMergeField Then
                   oField.Lock
               End If
           Next oField
           Set oStory = oStory.Next
       Loop Until oStory Is Nothing
   Next oStory
End Sub

Otherwise, you might consider a more drastic option.

Sub UnmergeThis()
' Written 29 August 2002 by Charles Kyle Kenyon
' Updated 23 September 2002 to attach normal.dot
' Remove merge codes from document, remove from merge status
'
   ' Test for template - in template only disconnect from merge but leave
merge fields active
   '
   On Error Resume Next
   If ActiveDocument.Type = wdTypeTemplate Then
   '
   '   Test for merge document - do not run if not merge document
   '
       If MergeTest() = False Then ' private function call
           Exit Sub
       End If
   '
   '   Disconnect template from merge data
       ActiveDocument.MailMerge.MainDocumentType = wdNotAMergeDocument
       Application.CommandBars("MergeK").Visible = False
       Exit Sub
   End If
   '
   '   Test for merge document - do not run if not merge document
   '
   If MergeTest() = False Then
       Exit Sub
   End If
   '
   Dim oField As Field
   Dim vMsgBoxResponse As Variant
   Dim sUserTemplates As String
   '
   ' Double check with user because permanent operation
   '
   vMsgBoxResponse = MsgBox(Prompt:= _
       "This will disconnect this document from the merge file." _
       & vbCrLf & "This cannot be undone." & vbCrLf & vbCrLf _
       & "Continue?", Buttons:= _
       vbQuestion + vbYesNo + vbDefaultButton1, _
       Title:="Continue?")
   If vMsgBoxResponse <> vbYes Then
       MsgBox Prompt:="No changes made to document.", _
           Title:="Merge connection still active."
       Exit Sub
   End If
   '
   '   OK to continue
   '
   Application.ScreenUpdating = False
   '
   For Each oField In ActiveDocument.Fields
       If oField.Type = wdFieldMergeField Then
           oField.Unlink
       End If
   Next oField
   '
   ActiveDocument.MailMerge.MainDocumentType = wdNotAMergeDocument
   '
   '   Disconnect from template - attach normal.dot
   '
   sUserTemplates =
Application.Options.DefaultFilePath(wdUserTemplatesPath)
   If Right(sUserTemplates, 1) <> "\" Then
       sUserTemplates = sUserTemplates & "\"
   End If
   ' sUserTemplates =
Application.Options.DefaultFilePath(wdUserTemplatesPath) & "\"
   With ActiveDocument
       .UpdateStylesOnOpen = False
       .AttachedTemplate = sUserTemplates & "Normal.dot"
   End With
   Application.ScreenUpdating = True
   Application.ScreenRefresh
'
End Sub