BKKですよね？？？

全日空のサイトに詳しく書かれています。JALも基本的に同じでしょう。BKKで入国せずに国内空港でできるのはエアラインとともに限られています。ですから、具体的書かないと・・・・。でも、はっきりとは書きたくなく、そこはかとなく漂う雰囲気から察して欲しいと言うことなのでしょうか？

海外客が入国（審査）せずに、国内にいる誰もがアクセスできる（パスポートチェックなしに）ゲートに行けたら、、、それは国という概念がなくなるある意味理想世界なのでしょうね。

ANA -> Thai domestic flights
(1) For transit to Phuket (HKT), Chiang Mai (CNX), Krabi (KBV), Koh Samui (USM), Hat Yai (HDY) by Thai Airways (TG) (except for TG flight number operating by Thai Smile Airways (WE))
After check-in at Bangkok Airways (PG) transit counter to Phuket (HKT), Chiang Mai (CNX), Krabi (KBV), Chiang Rai (CEI) and Samui (USM) by Bangkok Airways (PG), complete the immigration at transit inspection area for domestic flights and proceed to the boarding gate of connecting flights.

(2) For transit to other domestic flights other than the above
After Immigration, baggage collection and Customs, proceed to the boarding gate counter of domestic flights on the 4th floor.
Transit from other airline's international flights and Thai domestic flights to ANA
When you have not checked in to ANA flights at departing airports, please check in at ANA transfer counter (Transfer Counter EAST or WEST) on the 3rd floor and proceed to the ANA boarding gate.
*Except for transfer from a part of airline companies