services:
    mapping.listener:
        class: AcmeYourBundleEventListenerMappingListener
        tags:
            - { name: doctrine.event_listener, event: loadClassMetadata }

use DoctrineORMEventLoadClassMetadataEventArgs;

class MappingListener
{
    public function loadClassMetadata(LoadClassMetadataEventArgs $eventArgs)
    {
        $classMetadata = $eventArgs->getClassMetadata();
        $table = $classMetadata->table;

        $oldName = $table['name'];      // ... or $classMetaData->getTableName()

        // your logic here ...

        $table['name'] = 'new_table_name';

        $classMetadata->setPrimaryTable($table);

        // ... or add a field-mapping like this

        $fieldMapping = array(
          'fieldName' => 'about',
          'type' => 'string',
           'length' => 255
        );
        $classMetadata->mapField($fieldMapping);

$mappingListener = new MappingListener();

// ... maybe even modify the listener using reflection

$evm = $this->get('doctrine')->getManager()->->getEventManager();
$evm->addEventListener('loadClassMetadata', $mappingListener);

doctrine:
    dbal:
        default_connection:   default
        connections:
            default:
                driver:   "%database_driver%"
                host:     "%database_host%"
                port:     "%database_port%"
                dbname:   "%database_name%"
                user:     "%database_user%"
                password: "%database_password%"
                charset:  UTF8
            customer:
                driver:   "%database_driver2%"
                host:     "%database_host2%"
                port:     "%database_port2%"
                dbname:   "%database_name2%"
                user:     "%database_user2%"
                password: "%database_password2%"
                charset:  UTF8

$em = $this->get('doctrine')->getManager('default');
  $em2 = $this->get('doctrine')->getManager('customer');

$customers = $this->get('doctrine')
    ->getRepository('AcmeCustomerBundle:Customer', 'customer')
    ->findAll()
;

$this->get('doctrine')
  ->connection('mysql://username:password@localhost/test', 'dynamic_connection');