Mod maker should have created it with skins in mind from the start, so we would avoid having to correct mods ourselves,
but I know where it's came from.
GT models as example (because that Civic is GT conversion) use separate meshes to make skin so, usually they aren't prepared to have one (not to mention sometimes broken UV1 and loss of UV2, 3 and 4 after unpacking).
This is what I mean. All of those stickers on car are separted meshes, don't belong to car skin.
View attachment 1515700
But after all 3D work with meshes, usually UV maps have to be made again anyway and at the end of the day it's easier for everyone when creator of mod makes it easy to skin.
IMO if I would ever make any more improvements for that Civic mod, I'd rather start from scratch, because it's not only uv maps, but 3d and ext_config are mess too.