Do right click on sheet tab and select view code and paste the below code. Return to excel and check... 
Private Sub Worksheet_Change(ByVal Target As Range)
With Target
If .Column > 2 Then Exit Sub
If .Columns.Count > 1 Then Exit Sub
If Len(.Value) = 0 Then Exit Sub
If .Column = 1 Then
If UCase(Trim(.Value)) = "ANNUAL" Then .Offset(, 1).NumberFormat = "@"
Else
If Not UCase(.Value) Like "##-[A-Z][A-Z][A-Z]" Then
MsgBox "Your entry should be like ##-MMM Only", vbCritical, "Invalid Entry"
Application.EnableEvents = False
.ClearContents
Application.EnableEvents = True
.Select
End If
End If
End With
End Sub
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