Is it possible to convert a Thai O-A retirement visa to an O retirement or O marriage visa, based on complete and verifiable documents, without leaving Thailand?

Any recommendations for an agent to assist in this process please.

No possible and any agent suggesting it is possible is way outside of reality. 

I recommend agents often however non O-A to non O in Thailand not possible 

 

Edit: completely missed the option of non O-A extension based on marriage. Took too much notice of thread heading. 

What @Pib posted is correct.

Sweet deal. 

No....can not.   

 

But you can switch from a O/A Retirement extension of stay to an O/A Marriage Extension of Stay.  As the underlying visa the original O/A visa will still be in place but the Extension of Stay will be based on Marriage vs Retirement....and this changes the required income and insurance requirements.

 

If doing a Retirement extension based on an underlying O/A the medical insurance is required along with the 800K deposit or 65K/month income.   But if switching to a Marriage extension based on an underlying O/A no medical insurance is required and only a Bt400K on deposit for only 2 months before applying or Bt40K/month income.  And after getting the Marriage Extension if you were using the 400K deposit method you can take the deposit balance immediately down to zero if desired "after getting the final extension stamp (don't drop below during the Under Consideration period which lasts for about a month after applying).  Or said another way you'll need to maintain at least Bt400K for 3 months over the year for a marriage extension vs 800K to 400K the entire 12 months for a retirement extension of stay.

  

Yea, there is a little more application paperwork required for a marriage extension like providing your original marriage certificate, a Kor Ror 2 marriage doc confirming you are still married which you can get easily/very cheap (a few baht) get at any district office in Thailand (I assuming you were married in Thailand), and 4 to 6 pictures of you and the spouse around/in your residence.   That's pretty much it in terms of additional paperwork over a retirement extension of stay.

 

Around three years ago I switched from doing a Retirement extension on my O/A for around 11 years to a Marriage Extension on my O/A in order to avoid the Thai medical insurance requirement.  And the marriage extension lower deposit/income requirement was nice.  

 

 

You cannot change the Non O-A to a Non O within Thailand, but you can change the reason for the extension from retirement to Thai spouse.
Even on the Non O-A, there is no requirement for mandatory Health Insurance for the reason of an extension of stay based on Thai spouse.

 

@Pib above, is perfectly correct.

Pib is sort of there and Liquorice is close, all depends on your local immy office. Very doable .... but TIT, depends on where you are. A mate of mine has just done it, immy officer asked why, wife doesn't like girlfriend .... stamp, stamp, stamp done .... with a smile.

????

Many thanks for your excellent advice @Piband @Liquorice.  Will give it a go.  Cheers

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