drupal-8-theme-override-in-module

/**
 * Implements hook_theme().
 */
function support_theme($existing, $type, $theme, $path)
{
    
    $commentField = $existing['comment'];
    $commentField['template'] = 'comment--field-support';
    $commentField['path'] = 'modules/custom/support/templates';

    $theme = [
        'support' => [
            'template' => 'support',
            'variables' => ['node' => null],
        ],
        'comment__field_support' => $commentField
    ];

    return $theme;
}