We will change the view of the organizations table, so you can see codes and sort/select them.
This table view is in a library snippet called library/Gems/snippets/Organization/OrganizationTableSnippet.php.
Copy this snippet to the folder application/classes/[yourproject]/Snippets/Organization
(you might need to create this folder first, use the correct capitalization!).
Adjust the class name to fit in the Zend folders/classes structure:

class Action_Snippets_Organization_OrganizationTableSnippet extends Gems_Snippets_ModelTableSnippetGeneric

There is only one function you need to overrule: the addBrowseTableColumns function.
The bridge model needs to be adapted, you will find lines like:

        (....)
        $bridge->addMultiSort('gor_add_respondents', $BR, 'gor_has_respondents', $BR, 'gor_respondent_group');
        $bridge->add('gor_accessible_by');

Add additional fields in the bridge model like this:

        $bridge->addMultiSort('gor_add_respondents', $BR, 'gor_has_respondents', $BR, 'gor_respondent_group');
        $bridge->addMultiSort('gor_code', $BR, 'gor_provider_id', $BR, 'gor_iso_lang');
        $bridge->add('gor_accessible_by');

This will add the codes to a multisort column.