You should probably have this in the texture.cfg
That's not needed, and won't work anyway, because the african marshaller doesn't simply have a different textures, but has also a different model.
But as I've said, there's no need to do anything and to even use the PainKit (unless the goal would be using the PaintKit to create a *new* face for one of the existing models), because those marshallers are already usable and referenced in the sim.cfg.
They are already selected and used by GSX, just the selection is entirely random, because the [fltsim.xx] section don't have any Couatl.icaoprefixes, so they can appear anywhere.