Dear Mr. Andreas,

You can use the following code to do what you have asked.

Dim sDocStyles As String

Sub CopyStyles()

   Dim oStyle As Style
   Dim sPrefix As String
   Dim oSrcDoc As Document, oTemplate As Document
 
  Set oSrcDoc = ActiveDocument
 
  Call GetDocStyles
   
  Documents.Open FileName:=ActiveDocument.AttachedTemplate.FullName, ReadOnly:=True
  Set oTemplate = ActiveDocument
 
   sPrefix = "Diss_"
   
   For Each oStyle In oTemplate.Styles
       If Left(oStyle.NameLocal, Len(sPrefix)) = sPrefix And oStyle.BuiltIn = False Then
           
           If InStr(1, sDocStyles, "|" & oStyle.NameLocal & "|", vbBinaryCompare) <> 0 Then
               ActiveDocument.Styles(oStyle.NameLocal).Delete
            End If
           
           Application.OrganizerCopy Source:=oTemplate.FullName, _
           Destination:=oSrcDoc.FullName, Name:=oStyle.NameLocal, _
           Object:=wdOrganizerObjectStyles
       End If
   Next oStyle

   oTemplate.Close wdDoNotSaveChanges
   
   MsgBox "Styles are copied successfully!", vbInformation, "Dear Andreas"

End Sub

'Gets the list of styles available in the document
Public Sub GetDocStyles()
   
   Dim iStylIdx As Integer
   
   sDocStyles = "|"
   
   For iStylIdx = 1 To ActiveDocument.Styles.Count
       sDocStyles = sDocStyles & ActiveDocument.Styles(iStylIdx).NameLocal & "|"
   Next iStylIdx
   
   If sDocStyles = "|" Then sDocStyles = ""
   
End Sub

I have created a ready-made template for you, but, this site don't have any features to send the files. So, i couldn't send you.. sorry buddy.. :(

Thanks,
parthiban,India