' Open the file to read from.
Dim readText() As String = File.ReadAllLines(path)
 
For i as integer = 0 to readtext.length-1
  'z.B. jede 5. Zeile 
  if (i + 1) mod 5 = 0 then 
     readtext(i) = "<spielID>" & readtext(i) & "</spielID>
  elseif '....
    '...........
  end if 
Next i

Dim filename As String = "F:\daten\....txt"
Dim lines As New System.Collections.Generic.List(Of String) _
   (System.IO.File.ReadAllLines(filename))
 
'.............. remove, removeat, insert usw
 
IO.File.WriteAllLines("F:\daten\out....txt", lines.ToArray)