Can I convert my OA multiple entry visa to a one-year O visa based on marriage without leaving Thailand?

If you are getting a year-long, multi-entry Non-immigrant Type O-A visa from a thai consulate in your country BEFORE you come here you will get stamped in for a year every time you enter the country.

IF you exit and re-enter the country BEFORE the visa expires you will get another year entry stamp <- letting you stay TWO years on a visa that is good for a year.

You CANNOT convert that to ANY O visa, AND you can't get a year extension on that visa type because you're married to a thai.

You either get a year extension based on being over 50 and by meeting the financial requirements based on retirement.

OR

You leave the country after you get the two years out of that visa and BUY a new 90 day Non-O based on marriage and apply for an extension off of that

Sadly You are nearly 100% incorrect :/