I'm not wrong. The OP asked if the Thai could apply for his visa in India or Turkey and you replied that he can apply at any embassy of a Schengen country. To what I said that this was not correct, you can apply only from a Schengen embassy located where you are resident, in that case Bangkok, not any Schengen embassy around the world.
Ok, I see the confusion. When I wrote "from a country" I meant "from a place where you aren't resident", and you understood "from the representative of the country" 😉
You can't. If you are resident in Thailand, you can't request a Schengen visa at an embassy located in the USA, Malaysia, Japan, or whatever country. Only in Bangkok.
Visa exemption is currently 45 days. You can get a 30-day extension of stay. You cannot use that extended stay date for you return ticket as the 30 days aren't yet granted to you when you apply for the COE.