Usually, the guidelines / instructions of the Department of Personnel & Training (DoPT) are applicable in the case of autonomous organisations of the Central Government. However, if your organisation does not follow the DoPT guidelines, then you’ll have to find out the relevant guidelines which are applicable to you.
Even otherwise, if your organisation is informing you that an employee cannot apply for a lower job, then you can ask your organisation to tell you about the relevant guidelines on the basis of which they are saying so.
In any case, the consolidated guidelines of the DoPT [No.28011/1/2013-Estt(C) Dated 5December, 2013 of the Government of India, Ministry of Personnel, Public Grievances and Pensions (Department of Personnel & Training)] on application through proper channel for another post are available at this link. You can go through these guidelines. It is mentioned therein that these guidelines are applicable to autonomous bodies too. There does not appear to be any restriction for applying for a lower post in these guidelines; but you can confirm from your organisation.
All other DoPT circulars can also be searched at this link by searching the relevant subject or providing other details.
Moreover, if you willing to resign and forego the benefits of the existing post (as you have said), then it should not be a big issue because you can resign first and then apply (though in this case, you’ll have some risk factor if you are not selected in that lower post).
Dr. Ashok Dhamija is a New Delhi based Supreme Court Advocate and author of law books. Read more about him by clicking here. List of his Forum Replies. List of his other articles. List of his Quora Answers. List of his YouTube Videos.