A quick glance over the code so far says no. But we'll find out. I'm doing it gradually because I have to set the stats over all the LI. All their lust, love, obed, inbt, addiction rate, etc. etc. Besides, I'm still farming for gear for Xenoblade X. I want to get a gear set that works for my build in and out of skell. The only thing left I haven't beaten yet is Telethia and I want to do that before I do Chapter 13 act 2.
But the save file, as I mentioned before, is in a pickle format. The pickle is not made just for games. It's made to hold data and code as exactly as-is as it can. So if you put in a negative value, it should hold it as a negative value.