I just realized something... You're thinking about the status as "charmed," and I'm thinking about it as "confused."
In later FF games, they are disparate, but in FFIV they are treated as one and the same.
Generally, when cast on the party, the visuals suggest charm... I'm thinking about the technique used by Lamia-types where the heart floats toward the character, then the character literally faces the opposite way and starts fighting for the enemy.
What few visuals we have for the status as cast on monsters suggests confusion more - with the little bird flying in a circle.
However, the spell is called "Charm," and the default FFIV effect on monsters suggests charm more than confusion.
The thing is, I like the idea of confusion more than charm. Erratic behavior by the confused fighter lends itself to the potential for extended status effects - if the chosen action is fight, then there's only a 50% chance that the fighter's own side is targeted, then of course the chance that self still isn't the target. Furthermore, there's a possible downside for the caster to confusion - if a monster casts a full cure on one ally under certain circumstances, there exists the possibility it might full-cure its whole party, just as there exists the possibility a confused Behemoth might Storm your party at any moment unprovoked. Charm status - simply flipping the "enemy" and "ally" bytes - would always benefit the caster greatly (pending success), since un-charmed monsters can't choose to whack their ally out of it, and the potential to abuse the system as in your behemoth example.
That being said, what you're suggesting (option 2, I mean, option 1 really would provide no gameplay benefits) would definitely be far easier to assemble...
Targeting bytes are bitwise, BTW, so the first monster in the battle - the one whose stats are stored at 7E2280 - is always "80," even if it's that monster acting. Whereas 00 works as "target self" for the party, I'm not positive it works that way for monsters. I struggle to think of any monster techniques that have a necessary self target (like "Hide").
I don't know, I guess I'll have to think about it a bit before I finalize the plan...
Anyone else reading this who might want to chime in thoughts and opinions?