Mandatory characters

OK, still working on this, and I have a few more questions.

What I want to do is make characters 03 and 06 mandatory during the flight to the Floating Continent. The problem is that using the code 99 01 48 00 brings up a party select screen that is totally empty, unless characters 03 and 06 happened to already be in the active party (in which case they appear, and are in fact mandatory).

I looked at the code that runs when the party select screen comes up before the Opera House event. I see the code there to add and remove characters from the party as needed, but when I try to replicate it, I still get a blank party roster. I'm thinking that I must be missing some inobvious command/subroutine that makes everybody appear. Any ideas?

Near as I can tell, B2 9F CB 00 is the "normal" party select code, which makes everybody appear, with nobody made mandatory. I thought that maybe I could simply make an edit to this subroutine, but frankly, I've never had a good grasp of how the subroutines work.