Adding a new grade to an existing bolt can be done with GAM Bolt Editor.
More information about how this tool is used can be found in the following FAQ : http://www.graitec.com/en/FAQ_view.asp?FAQID=997&Language=EN&Name=How+do+you+create+a+bolt+in+the+Graitec+Advance+Manager%3F
To add a new grade, you will need to add the grade, and then reconfigure the bolt to it while using the existing valeus from the 4.6 / 5.6 grades. Currently GAM Bolt editor doesn't allow to duplicate an existing grade, diameter, and just modify one parameter, so the new grade will be seen as a "new" bolt configuration, requering you to make the necessary settings to it.