How Can I Change My Non-Imm 'B' Visa to a Non-Imm 'O' Retirement Visa Without Leaving Thailand?

You would cancel your work permit, take that receipt and the termination letter from your employer stating you are quitting on xxx date to the immigration office.

You would cancel your current extension and immediately apply for a NEW yearly extension based on being over 50 (retirement) by meeting the financial requirements and submitting the appropriate documentation. They will issue the extension based on retirement right then.

So it most definitely CAN be done, it's just gonna take some coordination..

I would stop in to your immigration office and talk to them about it. You're NOT wanting to go from a Non-B visa to a Non-O visa so don't even mention anything like that or you'll get bad info.

You are only wanting to change the REASON for your extension from one based on employment to one based on being over 50 (retirement).

Okay, now that we sussed out you're on an extension (and not a visa) you COULD change the reason for your extension from one based on employment to one based on being over 50 (retirement).

BUT let's see if we can't help you out

Are you on the initial entry of a Non-B visa that you got from a thai consulate in another country

OR

Are you on a yearly extension of stay based on employment from the immigration office

you cannot change Non-Immigrant VISA types inside the country :/