Apparently it was published today in the Thai gazette. If that is true then you definitely don’t need the pre flight PCR test, but you may want to do a PCR or lFT test just incase. As you don’t want to test positive on arrival.
for you to just be classed as a transit passengers so your luggage is sent all the way to HK each flight needs to be on one ticket. You can’t purchase separate tickets
As far as I know if you are not entering SG you can transit through SG but have to have a negative PCR test within 48 hrs from departure, and all segments must be on the same ticket.
If you wish to enter SG then you have to fly on a VTL flight from BKK with the negative PCR test also