Data = Replace$(Data, Text1.Text, "funciona", , , vbTextCompare)

Private Sub Command2_Click()
Dim Data As String
Open ("C:\ejemplo.txt") For Input As #1
   Line Input #1, Data
Close #1
Data = Replace$(Data, "HOL", Text1.Text, , , vbTextCompare) 'Esto es para que no haga diferencias entre Mayusculas y minusculas...
Open ("C:\ejemplo.txt") For Output As #1
   Print #1, Data
Close
End Sub