For each formfield you want to trigger the unlinking with, add the line:
FmFld.ExitMacro = "Unlink"
after the last existing line referencing that formfield. Supplement that with the following macro:
Code:
Sub Unlink()
With ActiveDocument
If .ProtectionType <> wdNoProtection Then
.Unprotect Password:=Pwd
End If
.Fields.Unlink
End With
End Sub