With Final Fantasy XIII, I'd probably give enemies different stagger requirements so the game doesn't get quite so repetitive, maybe add a central town area like Rabanastre so there's some downtime (since the party's a gang of fugitives, maybe they could have a hideout in the slums a la Sector 7). For FFVIII I'd have them scrap the plot past disc 1 and make it a story of a bunch of young soldiers fighting Demon-witch Hitler. Keep the cool modern 1950s aesthetic they had going, keep out NORG or Esther, focus on making Squall slowly open himself up rather than jumping to him suddenly caring about other people, keep Laguna involved SOMEHOW. Also, ax junctioning, or at least add more conventional JRPG leveling features.