Check for default values, Prompt for default values, Double click change default valu

There are 4 ways that I can think of to do it. If you only have those textboxes on the userform, a class could be use. The Tag property for the textboxes could be used. You could check each as focus was lost. Or a loop like this:

Private Sub CommandButton3_Click()
  Dim c As Control
  Dim ans As Integer
  ans = vbNo
  For Each c In Me.Controls
    If TypeName(c) = "TextBox" And c.Value = "" Then
      ans = MsgBox(c.Name & " has no value.  Insert the default?", vbYesNo)
      If ans = vbYes Then
        Select Case c.Name
          Case "TextBox1": c.Value = "My Default Value"
          Case Else: 'do nothing?
        End Select
      End If
    End If
  Next c
  Unload Me
End Sub

You can change the c.Name in the MsgBox to say c.ControlTipText if you want to add a descriptive name for your textbox for the message. Of course you would need to change TextBox1 to the name of your textbox and add other Case lines for each of the default values that you want to insert if they click Yes.