Within the Add-in, you can sign out from an Excel instance.
To note: you must close out of each open Excel instance individually, since all open Excel instances will not close automatically when you sign out from one. If you do not close each Excel instance individually, the next time you open one Excel instance, you will automatically be signed-in to all the Excel instances.
After signing out, you will still see the Studio tab in the ribbon, and you can click on Log on when you need to work in the Add-in again.