need to over-write a shared service variable..

Hi,

I use a service that returns a default value defined in config file, but I need on runtime to update this value in order to use it later. Unfurtunately, it's always the default value that is returned.. my code:

-config.ini

    [helpers]
    stHelper = defaultValue

• services.php

    $di->setShared('helperBag', function() use ($config) {
    return $config->helpers;
    });

• controller.php

    public function modifyDefaultValueAction() {
            $this->getDi()->getHelperBag()->remove('stHelper');
            $this->getDi()->getHelperBag()->set('stHelper', 'newValue');
    }
    //later
    public function getModifiedValueAction() {
            $this->view->modifiedValue = $this->getDi()->getHelperBag()->stHelper;
    }
    });

what's wrong?