How can I change my O-A visa to an O visa while in Thailand?

Changing an O-A VISA and/or extension of stay from an O-A visa to an O visa.

Sorry to burst your balloon or piss on your parade BUT there is NO way to go from either an O-A visa or a yearly extension off an O-A visa to an O visa inside the country without leaving ONCE..

Think of an O-A visa and the first link in a chain and the yearly extensions as other links connected to it. In order to switch to a Non-Immigrant Type O visa <- (the type that does NOT require health insurance) you need to "break the chain" of extensions leading back to the original O-A visa.

You might as well get the two years of stay out of the O-A visa like most people do, THEN you need to exit the country without a re-entry permit during that second year.

Now FIRST you have to check with your immigration office as far as if they will issue in country 90 day Non-Immigrant Type O visas (not every immigration office can do it) AND you need to see how long the application for the Non-O visa goes under consideration (most offices are 14 days but some are 21, meaning you need at least that amount of time on your current entry stamp to pull it off). The cost of an in country 90 day Non-Immigrant visa is 2000baht. They are sold as NO ENTRY <- meaning there isn't a single or multiple entry with it because you're already IN thailand.

Assuming you went to the immigration office and found out they DO in country conversions AND that you do meet the financial and documentation requirements to apply for it;

You can go to a border bounce out and back to get a 30 day visa exempt entry OR you can go to a thai consulate and get a single entry tourist visa OR you can get a 90 day non-O visa <- if you can find a consulate that will sell one to you.

Once you have either a 30 day visa exempt entry stamp OR a 60 day tourist visa entry stamp go immediately back to your immigration office with the required documentation (bank letter, TM30 receipt, lease, copies etc) and apply for the 90 day non-O visa based on being over 50 (retirement). It will go under consideration for how ever many days that office requires then you go back and get the Non-O visa inked in with a USED stamp on it (seeing as you are already here) and you get a new 90 day entry stamp (dated from the date you applied for the Non-O).

Then you just wait until you have the required time left on that new 90 day stamp and apply for a year extension of stay like normal by meeting the requirements.

NOTE: IF you apply for the in country 90 day Non-O visa and need to leave the country you WILL need a re-entry permit to keep your current entry stamp 'alive' AND you would need to be back before the under consideration period runs out.

That is the ONLY ways to go from an O-A visa or extension to first a Non-O visa and then to a yearly extension.