Update for potentially concerned readers:

I slogged back to the Nong Khai border by train, since the only thing everyone I asked agreed on was that they could only change things like this at the original point of entry. Brought a translated letter to the re-entry permit room. Tried to be as respectful as possible. Everyone’s pessimism had me expecting the worst. A few people silently read the letter before one officer just said ‘okay mister!’ Then he took a pen and a stamp and changed the date and entry type so that it’s as if I entered on my tourist visa and not the exemption, thus giving me 60 days starting from my original entry 50 days ago. Then he let me leave, no fine or anything.

Maybe I got lucky but dreams do come true!

@Galen ******

uh, I didn't mean it sarcastically, he's obviously a great source of knowledge and a person I should be directing my questions towards. I wasn't trying to make a statement in any way. So, uh, yeah.

@Tod ********

one more question, since you're the guru of this! Do you think it's better to wait until immigration is open again and handle things through that channel? Or go to the border asap and leave and try to re-enter? The whole reason I got a tourist visa in the first place was they told me at the border it was better than doing another exemption again. :(

@Edward *******

well at this point it was a new passport, there were two other stamps, two full page visas and they had me fill out a form where I had to put the number of the visa I had just received. This was a lottery that was hard to lose

@Ellie ******

yeah, the visa is not struck through, and the stamp does not say TR. So this means nong khai won't fix the stamp and I can't get them to consider this my tourist visa stay? My only option is being charged with an overstay? That is... Unfortunate

So you're saying it's not good to go anywhere here in bkk? The only way to avoid an overstay is hoof it back to nong khai?

@Tod ********

yup, after entering about 60 countries on hundreds of flights, I guess I developed a blind spot since I never had a stamp problem, I had the two month date on my calendar, and even finding the right stamp in my passport can be difficult. And I thought they had all the info digitally anyway!