Paragraph 11 of article 4. of Paris Agreement clearly states that countries have the right to replace their NDC at any time. Nevertheless, it recommends that countries should do so with a view (that is, they are encouraged to) to make the NDC more ambitious.

Thus, if countries think that they would like to revise their INDC, they can do so upon submission of the instrument of ratification. However, if countries prefer to submit their instrument of ratification at the earliest, they can also submit a revised NDC at a later date.