Synchronizing a RDS instance with another RDS instance

I have a database on an RDS Instance (master) that needs to be synchronized to another RDS instance (slave). I created a read-replica for the first one, but that is created as read_only so I cannot do any operations on it.

Basically, I'll need to create a few other databases on the slave instance as well so that needs to be non-read-only. I'll also need to setup sync to happen once daily.

I am using MySQL 5.6+.