Many years ago, there were this sandbox program (before it became an addon to windower). It would basically make copies of POL. The great thing about that was that you could add different characters to each instance of POL. Today you can add 4 at max, but with this sandbox program you could add 4 for each instance. Logging in my 5th and 6th char today, I need to use the guest function which is tedious and annoying. Does anyone still have this program, and does it still work?
Alternative options I've seen people use:
Use multiple clients (US/JP/EU)
Batch file to switch the config out
Or my solution (a bit of overhead, but hey), I play the game in VMs anyway, I just make a VM for each character, and toss them on their own screen, have controller locked to that session, have the settings set to where even if I have the VM run in the background and bring it back it won't crash (hell I've even managed to stay up from an accidental suspend once). Obviously if the host goes down everything else still does, but it also makes it easy to reinstall the host OS as all I'd have to do to migrate the guests is to copy the files and as I keep them on other drives anyway...