Well, PSIO has a working option for disc change, but requires a text file (which the PC setup can do for you) and ejecting and inserting the SD card again.
I would rather keep the disc images separate when possible, mostly for convenience and compatibility.
I did run across a disc combining method recently (links later), which I am dying to try out on PS2/POPS. Even that has another method, but I'm still exploring there. I'm only willing to combine on the games that require mid-game change though. I think I still have a save from Lunar that I could test when it comes to it, but I'll have to convert the save to get on my PS2 (save converting I did for Diablo using a couple programs, but I'll have to re-learn that).
Lunar would be a perfect game to test though.
I will link my findings later (it will be a few days to a week).
Multi Disc PS1 games (and save before change)
Re: Multi Disc PS1 games (and save before change)
...just another lost soul...