Can I cancel my retirement visa extension to switch to a marriage extension before the renewal date?

Sounds challenging !

All you can do is go to the immigration office you use and try it. I'd go "armed for bear" with all the documents you need to get a marriage extension (bank letter, bank book, TM30, map, photos, marriage certificates, thai wife, etc) with you and just act like it's totally normal to do this. AND if they say why tell them you might be leaving when this current extension comes up and you want to cancel this one and get get a new extension based on marriage NOW so it doesn't run out when you're out of the country :)

Make the officers talk to you not AT you thru your thai wife <- which means telling your wife to tell the officer to talk to you instead of running the show..

Good luck, take care,

I think it's possible. Cancel the extention based on retirement and immediately apply for the extention based on marriage. I know it can be done by cancelling a Non B extention.

Not sure on this one. Probably very office dependent. Some may let you, others many not. I guess the only way you’ll know for sure is to pay your local office a visit and ask.