Yes you can do that. There is no checked luggage, so there is nothing wrong with buying a train ticket to Paris, but getting of in Brussels.
Having said that, you might want to check other options. There is the cheaper train to Brussels. You can buy tickets for the train to Brussels at any Dutch railway station. This train is without reservation.
There is also the idbus with regular service to Brussels from Amsterdam.
If you are flying in to Amsterdam with KLM, there is also the option to continue your journey. As with some other train stations Brussels has an airport code (ZYR) and at some airlines it is possible to buy an airline ticket to ZYR. You would however continue your journey from Amsterdam airport to Brussels on the Thalys. The beauty of this trick is that when your incoming flight is delayed, they simply put you on the next train.