The macros below can be used to replace text in a text file, e.g. when you want to change a column separator in a text file before you import it into an Excel worksheet or after you export a worksheet to a text file.

Sub ReplaceTextInFile(SourceFile As String, sText As String, rText As String)
Dim TargetFile As String, tLine As String, tString As String
Dim p As Integer, i As Long, F1 As Integer, F2 As Integer
    TargetFile = "RESULT.TMP"
    If Dir(SourceFile) = "" Then Exit Sub
    If Dir(TargetFile) <> "" Then
        On Error Resume Next
        Kill TargetFile
        On Error GoTo 0
        If Dir(TargetFile) <> "" Then
            MsgBox TargetFile & " already open, close and delete / rename the file and try again.", vbCritical
            Exit Sub
        End If
    End If
    F1 = FreeFile
    Open SourceFile For Input As F1
    F2 = FreeFile
    Open TargetFile For Output As F2
    i = 1 ' line counter
    Application.StatusBar = "Reading data from " & TargetFile & " ..."
    While Not EOF(F1)
        If i Mod 100 = 0 Then 
            Application.StatusBar = "Reading line #" & i & " in " & TargetFile & " ..."
        End If
        Line Input #F1, tLine
        If sText <> "" Then
            ReplaceTextInString tLine, sText, rText
        End If
        Print #F2, tLine
        i = i + 1
    Wend
    Application.StatusBar = "Closing files ..."
    Close F1
    Close F2
    Kill SourceFile ' delete original file
    Name TargetFile As SourceFile ' rename temporary file
    Application.StatusBar = False
End Sub

Private Sub ReplaceTextInString(SourceString As String, SearchString As String, ReplaceString As String)
Dim p As Integer, NewString As String
    Do
        p = InStr(p + 1, UCase(SourceString), UCase(SearchString))
        If p > 0 Then ' replace SearchString with ReplaceString
            NewString = ""
            If p > 1 Then NewString = Mid(SourceString, 1, p - 1)
            NewString = NewString + ReplaceString
            NewString = NewString + Mid(SourceString, p + Len(SearchString), Len(SourceString))
            p = p + Len(ReplaceString) - 1
            SourceString = NewString
        End If
        If p >= Len(NewString) Then p = 0
    Loop Until p = 0
End Sub

Sub TestReplaceTextInFile()
    ReplaceTextInFile ThisWorkbook.Path & "ReplaceInTextFile.txt", "|", ";"
    ' replaces all pipe-characters (|) with semicolons (;) 
End Sub