We don't tend to do that because we don't think it makes any sense, for example if you had it so anyone who took over Kuat could build ISDs it would be kind of weird, and we already have the non-playable factions that can and do build those kinds of ships ships, without limiting their buildability to one planet. There are a few, such as the Bothan Assault Frigate (and in the Hunt for Zsinj GC, the amalgamated forces can build Hapan units), which we do have because they were actually made and used by and for that faction, the New Republic. All of the Corellian ships in the other mods are basically non canon designs, so we don't use them, and the other common ship that mods have like that is the clawcraft, which we already have for a major faction.