Dim F As Integer
Dim nCount As Long
Dim i As Long
Dim sLines() As String
 
F = FreeFile
Open "DeineDatei.txt" For Input As #F
While Not Eof(F)
  nCount = nCount + 1
  ReDim Preserve sLines(nCount)
  Line Input #D, sLines(nCount)
Wend
Close #F
 
sLines(13) = Text1.Text
 
F = FreeFile
Open "DeineDatei.txt" For Output As #F
For i = 1 To nCount
  Print #F, sLines(i)
Next i
Close #F