@Bobby *******
, okay, so you're on a year entry stamp from an O-A visa.
IF you were on a yearly extension from an O-A visa (which you are not) you COULD change the reason for your next extension from one based on retirement to one based on marriage
BUT
I always thought that the FIRST extension you got from a visa hand to be issued for the reason you got the visa <- which means because you have an O-A visa you would need to get that first yearly extension based on being over 50 NOT based on marriage.
I do know with 100% certainty (no matter who you think might know better) that IF you're on a yearly extension based on retirement from an O-A visa that does require insurance and the following year you change the reason for your extension to one based on marriage you DO NOT need to have insurance.
I think the only thing you can do IS pack up your thai wife and slog on over to your immigration office well before you need to get your extension. Show them your passport, let them see you're still on a year entry stamp from the original O-A visa and ask if you can get the first yearly extension in country based on marriage rather than retirement.