Where the configuration is saved and how to manually revert changes

Handyman saves the options that you specify in the /application/config/generated_overrides directory.

The file names reflect the first part of the configuration key. For instance, if you configure the option "concrete.user.username.allowspaces", then the file name will be concrete.php

In case you define an option value for a specific environment, then the file name will be prefixed with the name of the environment (for instance, for the "test" environment and the "concrete.user.username.allowspaces" option, the file will be named "test.concrete.php".

Those configuration files are very simple: they return a php array, whose keys are the remainig part of the option. For instance, the configuration key "concrete.user.username.allowspaces" will be represented in the "concrete.php" file as:

return array(
    'user' => array(
        'username' => array(
            'allowspaces' => true,

So, if you need to revert an option that breaks your site, you simply have to find the correct file in the application/config directory and change or remove the affected option.