If you plan on sending him to school in Thailand it would better if he was legal. We got our 1 year old son a O visa and then it was straightforward to add him to my Work Extension as a dependent. But if you only plan on a short stay, I'd follow Tod's advice.
Visas can't be transferred, only Extension of Stay stamps can. If it's visa vignette in your old passport, you just need to carry two until you get your new Extension. If it's an Extension stamp you can get it transferred at Immigration.
I don't think are any "new" rules or a new Immigration boss. If he has a valid WP already and presumably an Extension of Stay based on work, I'd say he doesn't have to do anything until it's time to extend again.
You're in the same position as me. Unfortunately unless you can get an Extension based on retirement (in which case your wife can piggyback like she does with your work extension) your options are limited. Do you have children at international school? If so, you might be able to get them an Extension based on studying at school, and piggyback on their extension.
As you're on an Extension of Stay based on work, this will end once you stop work and your WP is cancelled. You will have 7 days to leave. You should be able to change the reason for your extension to marriage, assuming you're married to a Thai and meet the financial conditions. As Billy Brown says, go and talk to your local Immigration office.