Can user edit denied registration request and resubmit it?

Users cannot edit denied a registration request, but they can resubmit a request by re-registering.

Registration requires approval only if the self-registration module is disabled under the System settings. For more information on how to enable/disable the self-registration module, please see this link.
Users can send registration requests only for a student role. For information on how the application looks from the student’s perspective, please watch this video.