Can I keep my Non 'O' visa after divorcing my Thai spouse?

You have a year-long, multi-entry VISA and when you got it you were married 🙂

Doesn't matter if you get divorced the next day after it was issued 😮

The visa is good until the date stamped on it even if the reason you got it changed

You can exit/re-enter every 90 days and use that visa until it runs out, and as Lloyd said, if you bounce out/back just before the VISA itself expires you can get a final 90 day entry stamp,

THEN

when that final stamp runs down you could apply for the year extension based on supporting a thai child at the immigration office for 1900baht

I wouldn't do anything until I maxed out the time I could get on that visa, no need to tell immigrations anything, as you don't GO to their office for anything, you bounce out and back every 90 days on the visa you have

Correct, as you have a VISA, you can use it up until the valid until date, so if you do a border hop a day or so before it expires, you can get nearly 15 months out of it.