I am no longer sure what you are trying to do. If you want to change the format of the placeholder text as suggested by your code example, then you only need to change the placeholder text style - once! - as in my last message.
If you want to do something if any of the content controls are displaying the placeholder text then
Dim CC As ContentControl
For Each CC In ActiveDocument.Range.ContentControls
If CC.ShowingPlaceholderText = True Then
MsgBox "True" 'do something
End If
Next CC
If as in your code sample you include Exit For outside the condition it will only process the first content control and ignore the rest. If you use Exit For inside the condition it will only process the first control that matches the condition.