I've attempted it a couple of months ago with Panzer Dragoon Saga and it didn't work. I previously tried swapping discs using the same method on Mednafen PSX and it worked just fine, so I know I was doing it right. Has anyone here actually succeeded to swap discs using m3u on Mednafen Saturn via Retroarch? I see some success stories on the standalone version, but not on Retroarch.
My error was the same as this dude's: https://forums.libretro.com/t/disk-swapping-issues-saturn-mednafen/6229 (Failed to set disc.)