Customising 'Select a label' tooltip in Outlook

Hi brendanm​ 

Unfortunately, you cannot modify the default tooltip text that appears when you hover over it. It is because, the text is hardcoded in Microsoft Information Protection Client which is a part of product UI and is not possible to be configured by the admin. However, I would recommend you configure Policy tip which are messages that appear inline when a label is auto applied or required. This can be configured in your own wording and proper justification.