Extremely possible and easy, turns out. Simply installing the newest version and loading my save worked perfectly, and indeed even fixed some problems that were previously happening. The new version letting you simply toggle features on and off on the splash screen that comes up every time you start it is super handy. And it includes the PS1 font without having to install a separate mod, which I had to do before.
I then of course continued the playthrough that I had been in the middle of. Going from around Madain Sari to Esto Gaza, as well as some sidequesting. And it just looks fantastic. And the OST tracks that they've redone are really tastefully done, imo (though they can also be toggled). Been having a blast, IX is just a lot of fun.
One thing that occurred to me while playing, though, I am ALWAYS turned around on IX's world map. Of course I don't know the map like the back of my hand the way I do FF7, but still, anytime I set off for a destination I always originally head off in the wrong direction. And even looking at the map it it takes me a couple seconds to even place where something like Alexandria is. And I tried to figure out why this is the case.
Is it the artificially short draw distance you have for awhile due to the Mist? Is it a more severely angled camera? Is it just that you go through a lot of areas that mean you emerge on the world map a distance away from where you actually were?
I guess it must be that last one. After leaving Alexandria, you go through the Evil Forest before you reach the World Map. Then you go through the Ice Cavern, and a emerge in a completely different area. Then you leave Dali and arrive at Lindblum via cutscene. Then when you leave Lindblum you leave through the Dragon's Gate which isn't actually very close on the world map to the actual city. And then you're bouncing around the world through the Gargan and Fossil Roos.
I dunno, I'm just dreadful at navigating that world and found it interesting to think about. Especially since if you told me to go to Rocket Town I could navigate there more easily than I can navigate my house