How to permaguest joining units?

[Ansehelm]

Heyo homies,
So as you know in FFT, there are some units that join as "guests" and do not contribute to your party limit of 16.  In vanilla, this designation is ultimately temporary.  In my mod, I want to have 4 characters that can permanently join and fight in random battles, but will retain the "guest" flag so as to allow for up to 20 party members.  I don't see an option that influences this in patcher, is this an event-related thing, or how do I alter it?
Thanks

Edit: I ran into a thread talking about expanding the party roster to 20, but apparently there are bugs with it, especially involving the Beowulf sidequest.  Either way, it doesn't seem to be fully resolved there.
Also Edit: I realize I probably should have posted this in the "help" forum again. My bad

[Nyzer]

Save Formation & Join After Event should cause the unit to auto-join as a Guest after their first appearance.

Forcing them into future battles will require Save and Load Formation.

To be able to use the Guest freely (in random battles or other story battles they aren't forced into) will require the ASM for that while also using a spreadsheet (last I checked?) to block the player from deploying them during any story missions you want them forced into again. Jot5 does this with Agrias, Olivander, and Leesha.

This setup does work rather well, but it's not at all like using those last four slots like regular slots.

Also worth noting: you can also use event commands to check if a certain Unit ID is in the Roster and/or on the Field (implying you've deployed them). I made a non-battle event that performs such a check to see if a character is in the Roster, and if so it adds them in and adds quite a lot to the event. May or may not affect what you do here, but hey.

[Ansehelm]

Sweet, that's helpful.  Seems like a viable method then.  Looking at the pros and cons, I guess this system would incentivize retaining up to 4 permaguested units.  On the other hand, the other method, referenced here http://ffhacktics.com/smf/index.php?topic=7629.0 would give the player more choices as to who to keep, but at the cost of removing all guest joins and editing the Beowulf event conditions.  Furthermore it seems that this has the advantage of more potential room for monster breeding.