I seriously doubt that this will be enforced at HKT.

The HKT business model is to be able tag bags to final destination on separate tickets as it will allow pax to proceed directly to int. transit area at BKK as C.I.Q pax (you will get a C.I.Q sticker to put on your shirt, jacket etc to be able to BKK staff to identify you as pax proceeding airside to security checks and transfer area; immigration/passport control will be take place at HKT). PG and TG do this numerous times for each HKT-BKK flight without batting an eyelid.

Admittedly, this was pre-Corona practise but I doubt it has changed despite Phuket Sandbox, restrictions etc