I lived and worked there, and transgender farang were near zero. They are treated worse than kathoey or tom which isn’t a very high bar. You can get surgery done cheap and well, but it is usually cosmetic stuff (top surgery, generic facial plastic suegery) rather than more complex bottom surgery. And you can’t legally change your gender in Thailand - all those kathoey are still treated in paperwork as men.

As for fake documents, maybe. I knew people that had visuals convincing visas in visually convincing passports for the purposes of carrying around in Thailand. However in this day of magnetic and RFID digital passports, document theft is far more realistic and common than fakes.