Phuket immigration said this can be done at Satun, using an agent.
If it saves getting the health certificate (34,500 baht) and all the form filling hassle, I may do it next year. This year's extension was a horrendous pain given that for the last 4 years no health insurance has been necessary.
Finding out that the rules had changed so that I needed it, and getting it all done in two weeks, with three public holidays and two other national holidays during that time was stressful.
Fortunately the IOs at Phuket have been very helpful and got the insurance done in 2 hours, compared to the AXA rep. who needed 7 to 14 days. I don't blame the rep., but the IO had a direct line to the "boss".
So, has anyone done the change from OA to O?