Well, it's been a long time that I played Bos:sr, but It seems to me that kobayashi stayed on the party even after changing of module. And the script to put him into the party didn't removed anyone. So use an Item to trigger a script like this could help to add new companions, without removing the old ones.
And we're talking about extra party members, the characters, not a extra member to the party etc... (I know he also asked for that, but that's not the ask I answered), juste the fact to recruit more people etc...
But maybe I remember wrong, if that's the case, sorry °°