Hi Ed:
Years ago (IIRC, in FS2002, Peter McLeland reported success modifying airport display by putting "stub" airport BGLs in:
[FS install path]\
Addon Scenery\Scenery folder
...which at that time, was kept by nearly everyone in its original position within the FS scenery library default stack of Area layers.
When Jon Masterson (aka "Scruffyduck") and others began working more extensively with airports, they discovered that certain airport modifications worked in a specific and controllable manner when positioned at an even lower display priority as described by Doug above.
Also, as described by Doug above, one can still load (some) airport BGLs at a higher display priority (relative to other BGLs in the same folder), from within a scenery sub-folder Area layer positioned higher up in the scenery library, by using 'alpha-numeric' file naming.
And as you may know, _ALT BGLs for FS spawn altitude of a user aircraft adjusts for both normal and multi-player sessions at airports.
It is certainly a challenge to update airports when ICAOs, names, and even locations change since ACES last updated the FS database.
GaryGB