Can you switch from a retirement extension to a marriage extension in Thailand?

Suffice to say it CAN be done, go with your thai wife to the immigration office you use well before you want to get your next extension and get the hand out listing the document requirements so you can get it all compiled and do it in one try 🙂

Good Luck with it

you can indeed, you can change the reason for your extension to one from being over 50 (retirement) to one based on marriage to a thai on your next yearly extension application.

Go to the immigration office and get their hand out that lists the specific documents you need to get the year extension based on marriage

This sheet gives you a rough idea of what is required.