Can I switch from a non-OA visa to a non-O visa upon re-entering Thailand after my OA visa expires?

How long are you planning on staying this time? If you plan to leave again within a few months maybe just do the 45 days and extend. As you know getting the retirement visa and paying for a reentry stamp costs some money. If you are planning on hopping in and out it's a waste of your money

You won't enter on a visa on arrival, as that is not applicable to the US. You'll get a visa exempt stamp good for 30 days, that you can extend for another 30 days. I will assume you already have a Thai bank account in your name only as you've been living here before. Being you're letting the OA visa expire, and switching to a type O based on retirement after you get here, you are basically starting over from scratch, and as such you will be required to show that your bt800,000 in your Thai bank account came from a direct transfer from overseas in order to meet the initial financial requirement. For the bt65,000+ income a month method you must show 12 months of direct transfers of at least bt65,000 each month from an overseas source, as the US embassy no longer issues income statements. This might be the only problem I can see you might face. Just remember that there must be at least 15 days left on your entry date stamp in order to apply. Your Thai ID card means nothing unless you are a naturalized Thai citizen. If you own a condo then your house book is relevant, but only if you own a condo.