Replacing default global textures

I’m interested in trying something like what Rex and Zinertek have done with creating new global textures for airports (aprons, taxiways etc).

Where are the textures located within msfs for these, and how might one go about tinkering? I understand mods like this can go in the community folder but I’m not entirely sure what dictates an override for things like textures. (I’ve had a look and it wasn’t obvious, not that I’m above just giving it a punt).

As long as file names and path of your addon are the SAME as default ones, the addon will override the default ones.
This is how Rex and Zinertek,and every other add-on overriding default stuff, works

About where they are, the following are some places to start