Restoring to modified database
When you restore a database backup, it completely overwrites the prior database regardless of its contents. There is no merging functionality built into the SQL Server restore process.

If you need to merge the contents of two databases, or restore a particular table by itself, your best bet is to:


Restore the backup to a different database name, like Production_Restored
Copy the objects you want from Production_Restored into the Production database
Drop the Production_Restored backup when you're done


As you copy objects from one database to another, keep in mind that transaction logging is involved. If you copy a 50GB table from one of these databases to the other, the target database's transaction log will grow, fast. Your best bet there is to move the data across in batches. (And of course, there will be blocking involved as data is changed.)