I created a dummy database awhile back filled with data that I use temporarily to test and demo new stores as I build them so I have to essentially do what your talking about a lot.
Find the "Connections" directory in your site and the file called "PowerStoreConnection.php"
Then edit the follow details as needed as they correspond to your new database:
$hostname_PowerStoreConnection = "localhost";
$database_PowerStoreConnection = "xxxxxx";
$username_PowerStoreConnection = "xxxxxx";
$password_PowerStoreConnection = "xxxxxx";
That should do the trick. The other option is to simply give the new database the same name and login info when you create it.
Hope this is what you wanted.