How to Configure an AOS to access a different database [AX 2012]

You can connect an instance of Application Object Server (AOS) to a different database.
You may want to do this in the following situations:

1. You are moving from a development or staging environment to a production environment.
2. You are upgrading a Microsoft Dynamics AX system.

Before you can connect an AOS instance to a different database, you must make sure that the AOS account is the domain account or Network Service account that is associated with the AOS service.

Connect to a different database:

1. Open the server configuration utility. Click Start > Administrative Tools > Microsoft Dynamics AX 2012 Server Configuration. 
2. Verify that the AOS instance and configuration that you want to modify are selected.
   On the Database Connection tab, use the lists to select a server, database, and baseline database, and then click OK. When you are prompted, click Yes to restart the AOS instance.
   If you do not restart the AOS instance, it does not connect to the new database.
   
   

One limitations of Single AOS to connect multiple database is we can have only one AOS - Database connection at a time. One AOS cannot connect to multiple database at the same time.
Only multiple clients can connect to a Single AOS and AOS is responsible for all the Database CRUD operations requested by all the connected clients.