How can I select my current visa subcategory when extending my visa exemption in Chiang Mai?

I would suggest just going, tell them why as you enter the grounds. They will show you where to go, point you to the table where the form is and if you botch it, they'll help you. Good folks in CM.

The eExtension system (which is run by VFS Global for thai immigrations) never updated last year in July when they switched from 30 day free entry to 60 day free entry (and when the free entry stamp code went from ผ.30 to ผ.60-ม.17)

The choice you want under current visa category if you came in FREE stamp is "exemption visa" <- visa exempt 😉

AND

The choice you want for your current visa subcategory is the Por 30 day (ผ.30) because as I said there is no Por 60 Mor 17 (ผ.60-ม.17) choice 😮

and the New Visa - Sub Category is "Tourism (Exemption Visa)

I will just point out there is very little "bang-4-the-baht" (value) in terms of jumping thru all the hoops to apply for the eExtension, paying the 500 baht surcharge in addition to the 1900baht and then STILL having to show up at the immigration office with all your documentation to get the 30 day extension sticker stuck in (yes, eExtensions are stickers)

I would say seeing as you're in Chiang Mai that you just slog on over to the Central Festival Mall satellite immigration location and get the extension there without bothering with the eExtension process.

BUT

The choice is yours 🙂 to each their own. 🙂

P/S;

I will agree that in Bangkok (where there can be several HUNDRED people in the queue out at IT Square Laksi Plaza waiting to get their 30 day extension on free stamp (visa exempt) entries that the eExtension process for 500 baht is often times a far FASTER option to get the extension.

Apply, get it approved, go to the main office at Chaengwattana (3rd floor to the eExtension room) get the extension sticker stuck in. Many people are willing to pay the 500 baht (minimum service charge) so they don't have to queue up at the crack of dawn with the zombie horde at IT Square. 🙂

These are the choices you want