And if your first letter is not always T, you could have a worksheet event
handle the conversion--more than just formatting, the actual value changes:
If you want to try it, rightclick on the worksheet tab that should have this
behavior. Select view code and paste this in the codewindow:
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Cells.Count > 1 Then Exit Sub
If Intersect(Target, Me.Range("a1:a99")) Is Nothing Then Exit Sub
On Error GoTo errHandler:
With Target
If Len(.Value) = 6 Then
If IsNumeric(Mid(.Value, 2)) Then
Application.EnableEvents = False
.Value = UCase(Left(.Value, 2)) & "-" & Mid(.Value, 3)
End If
End If
End With
errHandler:
Application.EnableEvents = True
End Sub
Change that a1:a99 to just the range of cells you want modified.
Then back to excel to try it out.