@The_Steel_Lance, do you need to have multiple characters seize? Because that would be a little bit more complex than just changing who can seize, and both are complex, as they involve ASM hacking, which since you asked the question in the first place, I'm guessing you don't know. If you only need 1 person to seize, but you don't want it to be Lyn, the quick solution is to just turn whoever you want to seize into Lyn by copying their character data and the such, and in-game it'll look like X person will be seizing, when it was originally Lyn's slot (which is irrelevant to players).
That is exactly what I ended up doing. Thanks.