Concept: Swapping Characters

Yeah, there is a command for averaging their level with the other members, but I don't recall anything that would set it exactly. At most I want to say you can average it, then have it slightly higher or lower.

However, that still doesn't touch stats at all (esper bonuses). Limiting those seems to be pretty popular generally speaking, but with something like this you would save none of that. Which leads us back to the whole thing being more of a novelty as a whole. Bring up the average level, fill in two generic extras, run the final dungeon.
I'm not sure how far something like saving their stats/level could be done, even on the asm level, don't think there is anywhere to save that kinda data indefinitly.

Course all that is only an issue IF your switching them around (the data that is). If you get them (even the two extra guest slots) and never remove or replace them again, data saved. I guess the whole idea could be used as a "pick your team" sorta thing. Once the player has chosen what/who to fill their team out with, thats it.

As far as doing it? That's completly possible, the details are already around here somewhere on the finer points, just a matter of having the sprites in game and acessable, the events to switch around, and some adapting to the guest adder patch to make it slightly more permenent.