Currently, it is not possible to add custom filters to a request to eZ Recommendation, through the "yc_show_recommendations" twig function (and then in the recommendation-bundle/Resources/public/js/recommendationrestclient.js file).
For instance it should be possible to filter the results from eZ Reco functions of some fields (tags) using a submodel in YooChoose. But there's not possible to add custom filters like that currently.
Please make it possible to add a new parameter to the "yc_show_recommendations" twig function to add custom filters. Maybe a simple string where one can add parameters to the query (like "&tags=tag1,tag2&type=2").