If you are registered under VAT, you need to migrate to GST. However though registration certificate will be issued but you can still cancel your registration if GST is not applicable to you.
A List of different forms is articulated by Pulkit.
As per registration rules issued by government,
Every person registered under any of the existing laws, who is not liable to be registered under the Act may, within thirty days from the appointed day, at his option, submit an application electronically in FORM GST REG-29 at the Common Portal for cancellation of the registration granted to him and the proper officer shall, after conducting such inquiry as deemed fit, cancel the said registration.
So, even if you are registered under GST, you can apply for cancellation of registration by filing form GST REG-29 which will be made available once GST is implemented.
chatCommentsSo the option to cancel the migration or deregistration will be available only once GST is implemented. Good things client has the option to cancel registration. - Rahul Rai