Recommender models trained on historical observational data alone can be brittle when domain experts subject them to counterfactual evaluation. In many domains, experts can articulate common, high-level mappings or rules between categories of inputs (user's history) and categories of outputs (preferred recommendations). One challenge is to determine how to train recommender models to adhere to these rules. In this work, we introduce the goal of domain-specific concordance: the expectation that a recommender model follow a set of expert-defined categorical rules. We propose a regularization-based approach that optimizes for robustness on rule-based input perturbations. To test the effectiveness of this method, we apply it in a medication recommender model over diagnosis-medicine categories, and in movie and music recommender models, on rules over categories based on movie tags and song genres. We demonstrate that we can increase the category-based robustness distance by up to 126% without degrading accuracy, but rather increasing it by up to 12% compared to baseline models in the popular MIMIC-III, MovieLens-20M and Last.fm Million Song datasets.