Hi,
as far as I can say the answer is no. You need to back up the existing database (to keep the record) or create a new one with Active Directory integration so that you have the other one for historical record (audit, data, etc.). The other option would be to export the content/data of the existing database, create the new one and import data. But I am not sure it is worth the effort. I would go the way of creating new database with MS AD integration. If you need data from both for some reporting purposes then create an export from the old database and group it with the new data (Tableau, etc.).