You can now.
Customising confidence levels is a long standing feature request and we’re pleased to say is now available. You can set as many confidence levels as you want, edit the existing ones, delete levels that are not assigned to deals and, of course, view weighted pipeline values based on these confidence levels.
Since launching the new pipeline interface with drag ‘n’ drop features we’ve been focused on refining existing features. Custom confidence levels is just part of making the existing product better.