[Vb.Net] Modificare un'intera riga di un RichTextBox

[gibra]

Prova così:

 
    Dim aLines() As String = rtb3.Lines
    Dim i As Integer = 0

    For i = 0 To aLines.Length - 1
        If Mid(aLines(i), 1, 1) = "c" Then
            aLines(i) = Mid(aLines(i), 2)
        End If
    Next

    rtb3.Lines = aLines