How can the President ensure that the State of Sikkim adheres to the constitution of India and its existing laws?
The President can ensure that the State of Sikkim adheres to the constitution of India and its existing laws by:

1. Adapting and modifying any existing law in Sikkim, as necessary or expedient, within two years from the appointed day (clause (l)).
2. Ensuring that Supreme Court and other courts do not have jurisdiction over disputes or matters arising from treaties, agreements, engagements, etc., related to Sikkim before the appointed day, except for Article 143 of the constitution (clause (m)).
3. Extending with restrictions or modifications any existing enactment in India to the State of Sikkim through public notification (clause (n)).
4. Addressing and removing any difficulties that arise in implementing these provisions by making necessary adaptations, modifications, or other actions within two years from the appointed day (clause (o)).