Just been asked this question and I have no answer.

If the owner of the car has changed from an "O" visa to tourist or 30 day exempt, is he/she still allowed to take their own vehicle in and out of the country?

There is no visa requirement on the Thai side to take a car out of the country.

Moved to motoring forum for further discussion.

what about bringing your Thai car back in??

don't you need an "O" visa to own a car?

what about bringing your Thai car back in??

don't you need an "O" visa to own a car?

No. Even a visa exempt person can own a car. You do however need to have an address, in the form of address verification to put your name on a car title/registration.

Although you'll be fine, but if you ever had any problems with getting your car across the border, it's getting it out, not bringing it back in. To bring it back in just requires you hand back the temporary import form (green) to the Lao side, get your ITP stamped, then get your ITP stamped on the Thai side, while handing in both white temporary export forms, one of which is the conveyance (passenger form), which is usually hand-written.