You cannot cancel your domicile just by giving a self declaration. It is the decision of the State of Jammu and Kashmir that it will not participate in All India Counselling and you cannot undo your domicile just because you want to participate in the Central Counselling. Canceling your domicile is cancelling your permanent resident status in Jammu and Kashmir and forgoing all the ties with the State and that is not possible with a self declaration form. When you sign a self declaration form, you are stating that you are not eligible for appearing for Counselling in Jammu and Kashmir and Ladakh and hence you are not eligible to see admission in MBBS, BDS, Aush courses of Jammu and Kashmir and Ladakh. You are also mentioning that you do not hold the domicile of both Jammu and Kashmir and Ladakh. But when you hold the domicile of the State you cannot give a declaration that you do not hold the domicile. That is legally incorrect and you will be held for that. Legal repucursions aside, you cannot get a self declaration done if you hold the domicile of Jammu and Kashmir.