Can a single U.S. citizen change a NON-OA visa to a Non-O visa after one year in Thailand?

Nope you can't change an O-A visa entry to a Non-O visa inside the country.

I messaged you before on how someone starts the process of getting into the country on an O-A visa. It is NOT beyond the ability of most people.

BUT unfortunately we're not allowing posts of people who are outside of thailand wanting to get in at this time.

There are more than enough "foreigners abroad" f/b pages dedicated to people trying to get back that have great information and up to date stuff.

Join one of those groups (y)

Good luck, with it