Yes. The beginning of your Core Programme studies is a continuation of the Piscine, so it is much better for you not to interrupt the learning process. Nonetheless, if you know you might not be able to enroll in the school right after the Piscine, it would be fair to leave the spot from someone who is eager to start, and join a later kick-off date.
You can always discuss this with the 42KL staff members for other arrangements.