Yes. In the Add Customer modal search for the customer and open their details, then press Edit to open the Edit Customer form (first/last name, email, password, phone, birthday, cards on file, notes, etc.). Under Options in that form, tap Allergens or Dislikes to open a full-screen panel listing every allergen/dislike with a toggle; switch the ones that apply and press Save. These update the customer's profile, so menu warnings in Checkout As and on the customer website reflect them going forward.