In order to merge the A model textures into the D model:
- Copy desired texture.X (X=texture name or number) folder from the FA-18 to the CS_FA-18D airplane forder.
- Copy texture.cfg file from any D texture to the new texture.X folder (overwrite existing texture.cfg)
- Copy from the A aircraft.cfg to the D aircraft.cfg corresponding  [fltsim.XX] section.
Make sure the new section has unique names and IDs and
model=d
texture=X