Admin generated backend modules are very useful, they are generating with all necessary code, they have some layout, all necessary actions are there and are easy to be modified. recently. You can even add default filter setting, although it's not as simple as editing generator.yml.

So, you can set default filter? Certainly not through table_method, this setting is for basic query, admin's filter is operating on later. To set default filter values, there are two methods you might want to overwrite. These methods are located in your module's moduleGeneratorConfiguration class located in your module's lib folder.

First method is getFilterForm(), which is used to serve filter form to be generated:

public function getFilterForm($filters)
{
    if(!array_key_exists('field_name', $filters))
    {
        $filters['field_name'] = 'value';
    }
    return parent::getFilterForm($filters);
}

Variable named $filters is array containing default values for filter form. Once we use filter, values get passed through filters to form, so it could show consistent field values. But if the field doesn't have value, we could set default one here. But that method only sets us default value on filter. If that's what you want, you got it, otherwise... overwriting this method is completely unnecessary.

Second method to look at is getFilterDefaults(), which is actually used to get default values for filter. These values are then applied both to filter form, and the query from table_method.

public function getFilterDefaults()
{
    return array('field_name' => 'value');
}

Method returns an array, that has same construction as the $filter variable from getFilterForm method. Now you can enjoy your admin's module list filtered by default values.