Option Explicit

Sub AdjustHistoricCodes()
Dim MyCodes As Variant, c As Long, LR As Long

LR = Range("A" & Rows.Count).End(xlUp).Row

MyCodes = Application.Transpose(Range("A2:A" & LR))

For c = LBound(MyCodes) To UBound(MyCodes)
    Select Case UCase(Left(MyCodes(c), 4))
        Case "CTCR":    MyCodes(c) = "N" & Mid(MyCodes(c), 5, Len(MyCodes(c)))
        Case "CTCP":    MyCodes(c) = "P" & Mid(MyCodes(c), 5, Len(MyCodes(c)))
        Case "CTWC":    MyCodes(c) = "CP" & Mid(MyCodes(c), 5, Len(MyCodes(c)))
        Case "CASM":    MyCodes(c) = "S / WR" & Mid(MyCodes(c), 5, Len(MyCodes(c)))
        Case "CANM":    MyCodes(c) = "N / WR" & Mid(MyCodes(c), 5, Len(MyCodes(c)))
    End Select
Next c

Range("A2:A" & LR).Value = Application.Transpose(MyCodes)
    
End Sub