Got a tentative non-b at Nakhon Pathom immigration today. All documents from me and my scool were accepted and I must return to get the stamp on the last day of my exemption extension. They made me sign 2 copies of papers acknowledging the overstay rules, so that has me a little concerned. To change 30+30 to non-b cost 2000 baht.
TLDR : Answer Summary
The user successfully obtained a tentative Non-B visa from Nakhon Pathom immigration by providing required documents. They are concerned about signing papers regarding overstay rules, which clarify that if they stop working, their visa extension will also cease. They also mentioned that it cost 2000 baht to change the 30+30 visa exemption to a Non-B visa.