@Tod ********
sent an email to LTR office asking about this. Reply as follows:
Referring to your inquiries, please see the answer as follows:
1. I visit in home country in July, and apply new passport while there (would be much easier and cheaper for me there than in Thailand via embassy in Bangkok )
Answer: Yes, it is okay to get a new passport form overseas.
2. I come back to Thailand in September, and show both the new passport and the old passport (with the LTR visa stamp) at immigration. I know that the validity of old passport would not be enough to enter, but I would have the new passport also.
Answer: Your current passport which contained LTR Visa is still valid. You have got a stay permit stamp equal to the expiration date of your passport which is 4 November 2025. Therefore, you can use it to enter Thailand in September.
3. I come to BOI office to transfer the visa in September after arrival to Thailand (old passport would have 1-2 months of validity left).
Answer: After arrived Thailand in September, you should transfer your LTR Visa to your new passport before your current passport expire on 4 November 2025.
Kind regards,
LTR Visa Member Team
So seems no different compared to how it would work e.g with non-o retirement.
Actually handy to have email to ask questions directly from them in writing.