If you're changing in Paris to go to Disneyland Paris, you’ll need a separate ticket called Billet Origine - Destination for any journey outside Central Paris (using RER or Transilien trains). You’ll need to choose Marne-La-Vallée – Chessy as your destination.
How to get from Paris Gare du Nord to Disneyland Paris:
Take Métro Line 4 in the direction of Mairie de Montrouge.
Get off the Métro at Les Halles.
At Les Halles, follow the signs and take the RER A to Marne-La-Vallee - Chessy.
How to get from Disneyland Paris to Paris Gare Du Nord:
Take the RER A from Marne-La-Vallee to Les Halles.
Take Métro Line 4 in the direction of Porte de Clignancourt and get off the train at Paris Gare du Nord.