@Carsten *****
yep, if you look in your passport the stamp will say "extension of stay permitted until" and you'd most likely have bought a re-entry permit stamp as well.
I'd say get the 90 day Non-O, come in, get thru quarantine or what ever and then when you got a month left on that 90 day stamp go apply for a new year extension using the 400K baht banked money you already have.