I've asked around a few international campuses if grad school enrollment qualifies for a student visa without leaving the country, and in international programs it does.

I've been told that once an application is accepted and fees are paid, administration would submit the student's documents to immigration, unlike Thai language schools, in which case you have to obtain the ED visa from outside the country. However, there is significant paperwork involved, so this is only an option for those who are or have been students. You need academic transcripts, thesis synopsis, letters of recommendation etc. As classes start July / August, application deadlines are at the end of June.

I am not allowed to drop school names so I won't. If there's anything wrong about this info, please correct it.