Great question. What you are referring to is the way RX tone is handled in the fire service firmware of the TK-790 and TK-X180. If left blank in the OST list, these radios will retain the RX QT/DQT that is entered in the channel edit section when OST is enabled and only the TX QT/DQT will change.
Normally for all other radios, when OST is enabled both the RX and TX tones are replaced by what is in the list regardless if the list has an entry or not. To move from area to area that would require a different RX tone (and still have access to the different TX tones to pick the repeater you want), you would have to leave the RX tone blank in the OST list and run the radio in carrier squelch. Not the best, but it works.
Flipping through the function manual for the NX-200 I do not see a reference where the new radios operate OST like is done with the fire service firmware so I assume it is the same as older Kenwood, the radios use both the RX and TX from the list.