Using existing database

I’ve seen several questions regarding access to a external database, but I would like to know if its possible to use the existing database without creating additional tables(SEC_USER, SYS_DB_CHANGELOG) which are required for CUBA platform?

Thanks in advance

Sure. Attach your database as an additional data store - then CUBA system tables will be created in the main database (you have to create it anyway), but your existing database will remain untouched.