I did and I thought I'd throw up my solutions for some further search options. This assumes you have access to your webserver to use some PHP code.
Option 1 - Set a Global Login
In your _config.php
Option 2 - Use the Environment Configuration file
At the top level of your site folder create _ss_environment.php
define('SS_DEFAULT_ADMIN_USERNAME', 'username'); define('SS_DEFAULT_ADMIN_PASSWORD', 'password');
Option 3 - Using a Member DataObject
In some page controller, config, or any interpreted php file:
$m = DataObject::get_one('Member', "Email = 'firstname.lastname@example.org'"); $m->changePassword('newpass');
All of these can get the job done. If you were thinking about trashing around the database and changing the hashes yourself I would recommend against it. SilverStripe uses salted SHA1 encryption which is no fun to try and create yourself just to overwrite in multiple tables.