What is the process for converting from a visa exempt entry to a Non-O visa for retirement in Thailand?

A friend from Sweden is currently on an O-A retirement visa. His permitted to stay stamp is the end of the month. He doesn’t want to do a new one year extension since the cost of the required insurance is more than he wants to spend. I’ve suggested he do a Border Bounce to cancel his O-A, return on 45 day visa exempt entry, convert to a Non-O visa and then do one year extensions on that. I’ve done the tourist to Non-O conversion myself but didn’t have the issue of a switching entry stamps first.

This is the general plan for the border bounce:

- Exit Thailand without getting a re-entry permit thus cancelling existing visa.

- Fly to Luang Prabang from Chiang Mai, stay a couple of nights and fly back.

- Return and get stamped in on 45 day visa exempt.

Alternatively, he could do the easier option of a Visa run day trip service from Chiang Mai to the Lao border at Chiang Khong to do a border bounce for the 45 day visa exempt entry.

The question is how soon he can apply to convert from visa exempt to the Non-O based on retirement? Can he do it right away? We’re aware of the 21 day requirement for Chiang Mai immigration. He already has the required affidavit from the Swedish embassy confirming his income. He also has a bank account but doesn’t maintain a significant balance since he has the retirement income verification. Note that he has a planned trip in late December (40th day of 45 stamp in). He’ll get a re-entry permit for his return on the Non-O.

Thanks!