BritTim

There is no urgency to get the stamp corrected immediately. When is your planned return from Phuket?

It means a pretty horrendous journey, but SkyScanner suggests that Gulf Air in November might bring you to CNX for a bit over 600 UKP from Heathrow via Bahrain and Singapore. Often these SkyScanner prices are mirages, and you are faced with long stopovers if using this Gulf Air routing. Still, you might want to check it out.

Were you entering with a visa, or expecting a visa exemption?

Although I do not always have much respect for UK consular services, I cannot imagine they would be unaware of the countries that will accept their emergency passports for entry. More of a problem, I think, is liable to be the Thai consulate in Savannakhet, and their policy on stamping visas into such passports. At land borders, care is needed on this. It should be possible in general (as should transferring the entry stamp at Nakhon Phanom immigration) but transferring stamps at minor land crossings can be tricky, especially if senior officials are not available. Better, as I suggested earlier, would be if the OP could fly out from a Bangkok airport. There, it is certain that they would be able to promptly accomplish what is necessary.

If you want 90 days, a Non O visa (to visit Thai spouse) is a good option. It is only the Non O visa (over age 50) that is contraindicated. Another option for your stay could be visa exempt (45 days) + 30 day extension + 60 days extension (to visit your Thai wife)

All the borders with Cambodia are open, but it is a pretty inconvenient trip from Hua Hin.

I am almost certain that the crossings in Kanchanaburi will be a non starter for some time. There are suggestions that the Andaman Club resort from Ranong may be open, but only useable by those with multiple entry Thai visas (no visa exemption on return). I cannot confirm any of this, but that might become a viable option soon.

I am surprised that you cannot use your old passport with its stamps as proof of your previous valid immigration status, and leave on the ETD. I appreciate that they cannot transfer some of the stamps from your old passport, but transferring the current permission to stay stamp should be possible. I think the problem is that Nakhon Phanom immigration really does not know what they are allowed to do, and simply refuses to do anything as the simplest solution. Assuming you can navigate the situation sufficiently to exit Thailand, the next question will be whether Savannakhet will agree to affix a multiple entry Non O into your ETD. One problem might be the validity period of the ETD (in which case a single entry would probably be OK) but they might have other objections. The issue with leaving Thailand could probably be overcome by flying out. Airport immigration has much more experience at dealing with these edge cases. However, I think you need to be clear about what will happen once you are out of Thailand. Maybe, easiest will be to return visa exempt, and switch back to Non O visas when you receive your replacement ordinary passport.

My understanding is that he does not have an extension. He has a valid multiple entry Non O-A visa. His plan is sound, but I would personally leave on the 7th, get a cheap room on the other side of the border for one night, and return the following day. The cost will be about the same, and I believe it is smart to avoid even short overstays (although a one-day overstay has no short term repercussions). EDIT: One other point occurs to me. Normally, leaving and returning on an unexpired Non O-A visa will give you a fresh one-year stay. Immigration at the border might refuse to give you this because of the lack of qualifying insurance. However, in that case, you should instead get the visa exempt entry you are looking for without incurring any overstay.

Some have problems, others do not. I think there are fewer people now for whom applying for a visa in advance makes sense. A single entry tourist visa buys you little, and a Non O-A visa or single entry Non O (over 50) tends to be a mistake. This is not because of the e-visa system per se, but because of changed requirements over time, and the current availability of a 45-day visa exemption.

That is why I suggested the use of an agent. It can avoid most of the hassle. However, if you are worried about the cost, your best bet is probably going to be a bus down to Malaysia.

We have been assuming that "visa" runs to Myanmar are not possible. Officially, all the land crossings are closed to foreigners. I wonder how this service via Ranong is able to overcome the issue. I wonder if there is some special arrangement with the Andaman Club on Thahtay Kyun Island where the security concerns preventing normal opening of the border crossings might not apply. A quick Google search does not reveal whether the hotel and casino is open for business.