Afaik no. When you flag an item via the "Custom" option you can enter a free-text value, however there is no way to reuse that, nor to clear any of the existing ones. Perhaps a third-party add-on can do this. Feel free to open an item on this over at the Feedback portal: https://feedbackportal.microsoft.com/feedback/forum/89a8afa3-2e1c-ec11-b6e7-0022481f8472