@OwlLord
That's exactly the issue. Tthe PartySwap item add-on adds the PartySwap item to your inventory when Disciple joins your party on Dantooine, so if you install the add-on only after Disciple has already joined you, the only way to get the PartySwap item is to use cheats or KotOR SaveGame Editor. If you don't want to use either cheats or a save editor, you need to reload a save before Disciple joins you for the mod's item add-on to take effect.
In general, when it comes to KotOR mods, It is not advisable to install mods when you're in the middle of your playthrough. It is also not advisable to mix Steam Workshop mods with installer-based mods, especially if you want to use a lot of mods. In case you missed it, the download page of PartySwap has already linked to a post on why Steam Workshop is not recommended for modding KotOR.