@Brian ********
no, the OA can be extended inside Thailand for another year exactly like Graham explained, and it is the same method as a type O extension, with the insurance requirement added. To switch to a type O you must exit the country when the OA expires, and start all over getting the type O 90 day entry stamp first then the one year extension. You can extend the OA inside Thailand, but it is no longer multi-entry unless you also buy the multi-entry re-entry permit, and it is only valid for the one year extension. You can not leave before it expires and return getting another one year stamp. It no longer works that way when extended inside Thailand