Using Script to open picklist inside the configurator

Inside a customized product configurator that we called NSI Configurator, we have a product picklist that is restrained by the Price list on the Quote header. This product picklist is the same that is used on the line items. On the line item, if the user doesn't have access to the product catalog, they will not be able to populate it on the part Number field. However, we noticed those same users [who don't have access to a product catalog], can manually type a product name inside the configurator and it would accept it. How can we restrain the product