CustomTheme\Module.php

<?php

namespace CustomTheme;

use Zend\Stdlib\ArrayUtils;
use Zend\ModuleManager\Feature\ServiceProviderInterface;
use Zend\ModuleManager\Feature\ViewHelperProviderInterface;

class Module implements ServiceProviderInterface,
    ViewHelperProviderInterface
{

    protected $config = array();
    protected $theme = null;

    public function getConfig()
    {
        return $this->config;
    }

    public function getAutoloaderConfig()
    {
        $autoLoaderConfig = array(
            'Zend\Loader\StandardAutoloader' => array(
                'namespaces' => array(
                    __NAMESPACE__ => __DIR__ . '/src/' . __NAMESPACE__,
                ),
            ),
        );

        $this->config = ArrayUtils::merge(
            include __DIR__ . '/config/module.config.php',
            include __DIR__ . '/config/theme.config.php'
        );
        $currentTheme = $this->config['CustomTheme']['current-theme'];
        if (!empty($currentTheme)) {
            require $this->config['CustomTheme']['theme-location'] . '/' . $currentTheme . '/Theme.php';
            $className = '\\' . $currentTheme . '\Theme';
            if (class_exists($className, false)) {
                $this->theme = new $className();
                if (method_exists($this->theme, 'getConfig')) {
                    $this->config = ArrayUtils::merge(
                        $this->config,
                        $this->theme->getConfig()
                    );
                }
                if (method_exists($this->theme, 'getAutoloaderConfig')) {
                    $autoLoaderConfig = ArrayUtils::merge(
                        $autoLoaderConfig,
                        $this->theme->getAutoloaderConfig()
                    );
                }
            }
        }

        
        return $autoLoaderConfig;
    }

    public function getServiceConfig()
    {
        if ($this->theme !== null && method_exists($this->theme, 'getServiceConfig')) {
           return $this->theme->getServiceConfig();
        }
        return array();
    }

    public function getViewHelperConfig()
    {
        if ($this->theme !== null && method_exists($this->theme, 'getViewHelperConfig')) {
           return $this->theme->getViewHelperConfig();
        }
        return array();
    }

}

CustomTheme\Original.php

<?php

namespace CustomTheme;

use Zend\ModuleManager\ModuleManager;

class Module 
{
    public function init(ModuleManager $moduleManager) {
        $theme = include __DIR__ . '/config/theme.config.php';
    
        try {
            $moduleManager->loadModule($theme);
        } catch(Exception $e) {
            //ignore "theme doesn't exist"
        } 
    }
    
    public function getConfig()
    {
        return include __DIR__ . '/config/module.config.php',
    }

    public function getAutoloaderConfig()
    {
        return array(
            'Zend\Loader\StandardAutoloader' => array(
                'namespaces' => array(
                    __NAMESPACE__ => __DIR__ . '/src/' . __NAMESPACE__,
                ),
            ),
        );
    }
}