josemarq that depends, when you haven't done anything with the Travel membership you can still downgrade to Free. As far as I know it's similar to when bunq introduced Premium; once you went for the new plans you could not go back. So, as far as I know you can freely move between Premium and Free (under the old terms) but as soon as you use the Travel plan you'll fall under the new terms and can not use Free anymore. 🙂
In short; it only applies to new customers, so it is not really without notice. 🙂