Sciences Po does not provide for a waiting list for graduate admission. The decisions of the selection committees are final and cannot be appealed.
Yes, you may apply again next year, through the same procedure or through a different one, as long as you meet the eligibility criteria.
Please note that you may apply a maximum of three times to a Sciences Po Master's programme, counting from the 2018 intake. A fourth application would not be processed.
No. If you have not been admitted, you cannot apply for another programme during the same academic year. However, you may apply again for the next academic year (up to three times, counting from 2018).