Off-hand, I recall doing turnarounds on TG to the following destinations:
AKL, ARN, BOM, CCU, DEL, DME, FCO, FUK, HAN, HYD, ICN, LAX, MAA, MAD, OSL, PEN, SGN, SIN, VNS, All domestic airports in Thailand, not to mention lots of turnarounds on SQ, OZ and other airlines. As you can see from that list, I've done turnarounds at most airports in India, of which many I would classify as being similar to KTM. I'm sure Indians and Nepalese would disagree that they're similar, but from my viewpoint as an outsider, the countries and thus things like airports seem more similar than different culture and business-wise.
Anyways, buy letting TG at BKK know about my turnarounds to India, they had on at least one occasion staff meet me at the door of the plane and guide me through the transit process, assuring me that it would be no problem and they'd hold up the returning flight if necessary to accommodate me. Even on flights where I didn't ask them to be notified, the staff was great in seeing that the unusual transit went smoothly. I assume you're arriving in business class, meaning you should be one of the first off the plane. Just be prepared with your documents and photo ahead of time. I recall there's now a reduced visa fee for passengers only staying a short period of time, so check into that to be sure you don't end up paying the full amount, unless things have changed recently.
Lastly, if you happen to be fond of flirting with flight attendants, as I am at times, doing a turnaround such as this, where TG's flight crew is the same both ways, gives a great way to break the ice with the FA of your choice. When they come and ask me why I'm returning immediately, I like to say something like, "oh, because I really wanted to see you again." Yeah, of course they know it's just B.S., but they usually end up chatting quite a bit with me for the rest of the flight if they're not unusually busy.