Yes you can do anything with PHP 
but what is your purpose.
You could just create another config.php file and connect from there?
Example below is calling the table $mycities from $wpdbtest_otherdb
$wpdbtest_otherdb = new wpdb('myaccount_cityuser', 'mypassword', 'myaccount_cities', 'localhost');
$wpdbtest_otherdb->show_errors();
$mycities = $wpdbtest_otherdb->get_results("SELECT name
FROM city
WHERE city.stadium = 1");
foreach ($mycities as $mycity) {
echo $mycity->name . '<br />';
}
Although the above example is dirty and not the most secure yet would call the data from the other DB as you might need…
PS Be more precise in your question.