Development models are unsupported anywhere. It's a hunting playground for all of us.
Regardless, I put a note here on the ACP issue.
You can do this a couple of ways
1. Regenerate your admin password using the installer. This is the fastest approach without editor.
2. With Editor that can run SQL remotely to your server. Install another v9 in localhost, copy admin_algo, admin_password, admin_salt there to your server. Keep a copy in your PC. Anything goes south, do a manual update your DB injection with this SQL into a file and run that url.
dbquery("UPDATE ".DB_USERS." SET user_admin_salt=:salt, user_admin_password=:pass, user_admin_algo=:algo WHERE user_id=1", [
':salt' => "[your_salt_here]", // copy value from localhost
':pass' => "[your_pass_here]", // copy value from localhost
':algo' => "[your_algo_here]", // copy value from localhost
]);
3. Downgrade your account and reset with admin password reset. To do that, you need to set ACP theme and find the password requirement in the text field to false. After that blank out salt, algo and type password as 123. Then login as 123 password in ACP. You'll get a lot of errors, but you can access admin password reset feature.