As long as your immigration office allows conversions to non-O visa, then yes you can apply to convert.

@Abdel ******

no. He has to get a new non-O visa. If he's already in Thailand then he'll need at least 14-21 days on his tourist entry and he'll need to get the list from his immigration office of requirements to convert. That will include a proof of funds requirement which is either bank balance or proof of income from the French embassy in Bangkok.

All non-O visas are valid for 90 days from the day they are issued.

That means you have 90 days to enter Thailand. Once you enter Thailand, you'll receive a 90 day entry stamp. Even if you enter the last day the visa is valid, you'll receive a 90 day entry stamp.

Why didn't he get a new non-O before he traveled back to Thailand?

Does he have a Thai bank account or can get income verification from the French embassy? If either of those he can apply for a new non-O from his immigration office if they allow in-country conversions.

@Munich ****

the past is irrelevant. New rules starting Monday. But no one really knows what they are yet

@Michael ******

the non-O visa does not have a health insurance requirement

No, there is not any customer service or emergency visa over the weekend. Only the embassy can issue the visa.

That should be fine to do. And you'll be setup for the future if you return and want to apply for extension.

If you enter on a non-O visa, the first extension must be based on the same reason that you got the visa for.

You say "waiting for my retirement visa to run out" so if you actually mean that, the 90 day non-O visa based on retirement, then no, you cannot switch to marriage because the extension must be based on retirement too.

But if you actually mean that you're waiting for your 1-year extension based on retirement (an extension is not a visa), then yes, you can apply for your new extension based on a different reason as long as you meet the requirements.

The only 6 month visa I know if is the multiple entry tourist visa. A non-O visa is only a 90 day visa.

So I really have no idea what type of visa you had or have, and what's actually in your passport as far as permission to stay in Thailand?